Biml Master-Child package connections - sql-server-2008

Question

In a 2008 BIDS/SQL Server/SSIS dev environment (along with BIDS Helper v1.70), I'm trying to create a biml master package that executes the child packages already built under Rootnode. Also using a config file to be able to run the entire process on different servers.
Config File
?xml version="1.0"?>
<DTSConfiguration>
<DTSConfigurationHeading><DTSConfigurationFileInfo GeneratedBy="XXXXXX" GeneratedDate="7/28/2016 1:28:29 PM"/></DTSConfigurationHeading>
<Configuration ConfiguredType="Property" Path="\Package.Connections[dw].Properties[ConnectionString]" ValueType="String">
<ConfiguredValue>Data Source=imsqldv50s\euc;Initial Catalog=CDODW;Provider=SQLNCLI10.1;Integrated Security=SSPI;</ConfiguredValue>
</Configuration>
<Configuration ConfiguredType="Property" Path="\Package.Connections[PkgFile].Properties[ConnectionString]" ValueType="String">
<ConfiguredValue>\\IMSQLDV50s\EUCPACKAGES\CDODW\Load CDODW Tables Biml\</ConfiguredValue>
</Configuration>
<Configuration ConfiguredType="Property" Path="\Package.Variables[User::ChildPackagePath].Properties[Value]" ValueType="String">
<ConfiguredValue>\\IMSQLDV50s\EUCPACKAGES\CDODW\Load CDODW Tables Biml\</ConfiguredValue>
</Configuration>
</DTSConfiguration>
The building of the child packages has been tested and passed. Now we are attempting to build the Master Package.
05-load-edw-master.biml
<Biml xmlns="http://schemas.varigence.com/biml.xsd">
<Packages>
<Package Name ="Master EDW Load" ConstraintMode ="Linear">
<PackageConfigurations>
<PackageConfiguration Name="dw">
<ExternalFileInput ExternalFilePath="C:\SSISConfig\CDODW_ETL_Load.dtsConfig" />
<ConfigurationValues>
<ConfigurationValue DataType="String" Name="dw" PropertyPath="\Package.Connections[dw].Properties[ConnectionString]" Value=""></ConfigurationValue>
</ConfigurationValues>
</PackageConfiguration>
<PackageConfiguration Name="PkgFile">
<ExternalFileInput ExternalFilePath="C:\SSISConfig\CDODW_ETL_Load.dtsConfig" />
<ConfigurationValues>
<ConfigurationValue DataType="String" Name="PkgFile" PropertyPath="\Package.Connections[PkgFile].Properties[ConnectionString]" Value=""></ConfigurationValue>
</ConfigurationValues>
</PackageConfiguration>
</PackageConfigurations>
<#=CallBimlScript("cbs-pkg-params-variables.biml", "No Table", "master-load", "","","")#>
<!--
<Connections>
<Connection ConnectionName="dw" />
<Connection ConnectionName="PkgFile">
<Expressions>
<Expression PropertyName="PkgFile.ConnectionString">#[User::ChildPackagePath]</Expression>
</Expressions>
</Connection>
</Connections>
-->
<Tasks>
<#=CallBimlScript("cbs-sql-audit-begin.biml", "master-load")#>
<Container Name="SEQ Load Dimensions" ConstraintMode="Linear">
<Tasks>
<# foreach (var package in RootNode.Packages.Where(pkg => pkg.GetTag("type")=="load-edw-dim").OrderBy(pkg => pkg.GetTag("LoadOrder"))) { #>
<ExecutePackage Name="EP <#=package.Name#>" DelayValidation="true">
<Package PackageName="<#=package.Name #>" />
</ExecutePackage>
<# } #>
</Tasks>
</Container>
<Container Name="SEQ Load Facts" ConstraintMode="Linear">
<Tasks>
<# foreach (var package in RootNode.Packages.Where(pkg => pkg.GetTag("type")=="load-edw-fact").OrderBy(pkg => pkg.GetTag("LoadOrder"))) { #>
<ExecutePackage Name="EP <#=package.Name #>" DelayValidation="true">
<Package PackageName="<#=package.Name #>" />
</ExecutePackage>
<# } #>
</Tasks>
</Container>
<#=CallBimlScript("cbs-sql-audit-end.biml")#>
</Tasks>
<Annotations>
<Annotation AnnotationType="Tag" Tag="type">master-load</Annotation>
</Annotations>
</Package>
</Packages>
</Biml>
<## template language="C#" tier="5"#>
The Connections have already been defined in a tier 1 file
After generating the packages, I note that the Biml engine creates Connection Managers using a convention "_" + Master Package Name.SequenceContainerName.ExecutePackageName, with a connection string pointing to the local file path. And it's doing so "under the covers" as there is no clue in the expanded biml file of how it's done!
Is there a nice simple way to interject a passed-in file path from the config file that can be recognized and used to build each FileConnection's data? I thought it would make sense to store the relevant file location in a variable (fed from the config file) and somehow use that to develop the ConnectionString from the package name garnered from the foreach snippet, but the engine doesn't appear to like that.
Any help is appreciated.
Thanks!