DECLARE @FullPathAndName varchar(100)  
SET @FullPathAndName = 'C:\DBA_Share\SSRS\Output\MyReport.rpt'

DECLARE @xVar XML 
SET @xVar = 
'<package name="\File System\ReportToExcel" owner="sa" runAs=""> 
    <variable name="Cnfg_ReportPath" value="C:\DBA_Share\SSRS\"/> 
	<variable name="vSourceQuery" value="select * from dbo.sometable"/>
	<variable name="vFileName" value="@FullFileName"/>
</package>'

DECLARE @price money=2500.00
SELECT ProductID, Production.ProductModel.ProductModelID,CatalogDescription.query('
declare namespace pd="http://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelDescription";

       <Product 
           ProductID="{ sql:column("Production.Product.ProductID") }"
           ListPrice="{ sql:column("Production.Product.ListPrice") }"
           DiscountPrice="{ sql:variable("@price") }"
        />') 
FROM Production.Product

DECLARE @FullPathAndName varchar(100)  
SET @FullPathAndName = 'C:\DBA_Share\SSRS\Output\MyReport.rpt'

DECLARE @xVar XML = ''

SELECT @xVar = @xVar.query('for $x in ("") return
<package name="\File System\ReportToExcel" owner="sa" runAs=""> 
    <variable name="Cnfg_ReportPath" value="C:\DBA_Share\SSRS\"/> 
	<variable name="vSourceQuery" value="select * from dbo.sometable"/>
	<variable name="vFileName" value="{sql:variable("@FullPathAndName")}"/>
</package>')

SELECT @xVar