Using Dynamic SQL in a WHILE Loop - sql-server-2008

Question

I work for an Insurance Company and creating a custom application. When we apply a coverage to a policy it is stored in a table with a Limit, Deductible, and Premium field. However, there are many coverages that do not follow the norm. They use different fields for Limit, Deductible, and Premium and are even stored in different tables. (Don’t ask why and don’t even try to understand the fact that they are STILL doing this so I need to leave logic to allow for additional coverages like this.) There is also no rhyme or reason to what fields they choose so varies greatly.
So, we have decided to create “LookUp” tables that will store all the information we need for a coverage. This avoids numerous joins – we were having issues with speed and performance of the application.
I need to find a way to prepopulate all these fields into a table. I would like the best option performance-wise. This will end up being a Nightly job – so when we receive a new snapshot of data we will run this query and prepopulate/update the values of the table.
I have the following code, I loop through this for each policy, essentially 614,000 time each night...It takes a LONG time to run.
Is there a better way for me to do this?
SELECT #SQL = N'SELECT #Limit=' + ISNULL(Limit, '''''') + N',#Deductible=' + ISNULL(Deductible, '''''') + N',#Premium=' + ISNULL(Premium, '''''') + N' FROM PHI_PIJ.dbo.ASBYCPP' + N' WHERE ' + PolicyNum + N' = ''' + #PolicyKey +'''' + N' AND BYAOTX' + N'='''+Coverage +''''
FROM PolicySummary.dbo.Coverage
WHERE Coverage = #Coverage
AND LOB = 'BOP'
EXEC sp_executesql #SQL, N'#Limit nVarChar(255) output,#Deductible nVarChar(255) output,#Premium nVarChar(255) output', #Limit output, #Deductible output, #Premium output
UPDATE PolicySummary.dbo.CoverageLkup
SET Limit = #Limit, Deductible = #Deductible, Premium = #Premium
WHERE CovAbbrev = #Coverage
AND PolicyKey = #PolicyKey
Here is what is inside my While Loop:
SELECT #SQL = N'SELECT #Limit=' + ISNULL(Limit, '''''') + N',#Deductible=' + ISNULL(Deductible, '''''') + N',#Premium=' + ISNULL(Premium, '''''') + N' FROM PHI_PIJ.dbo.' + [File] + N' WHERE ' + PolicyNum + N' = ''' + #PolNum +'''' + N' AND ' + #CovField + N'='''+Coverage +''''
FROM PolicySummary.dbo.Coverage
WHERE Coverage = #Coverage
AND LOB = #LOB
EXEC sp_executesql #SQL, N'#Limit nVarChar(255) output,#Deductible nVarChar(255) output,#Premium nVarChar(255) output', #Limit output, #Deductible output, #Premium output
INSERT INTO #OptCov2 VALUES(#Coverage, #Description, #LOB, #Limit, #Deductible, #Premium)