Add amount once per grouping in SSRS

Question

I am working in Visual Studio 2008 Report Builder and am trying to change how a report is displaying data. Suffice to say the report query outputs generally like below. What I want is a sum of the Credit value only once for each JournalID. I'm trying to avoid custom code, but since everything I've tried like nesting aggregates or other conditions seems to be failing, I may have no other choice. Right now I have a row group over JournalID, displaying GLAcct,GLDate and Credit once, then detail lines for VendorName & InvoiceDate. The detail lines only appear when InvoiceDate is not NULL (else I'd have a blank detail line for each entry). It should be obvious by now, but not all these entries have detail lines.

GLAcct      GLDate          Credit      VendorName      InvoiceDate     JournalID 
1010-000    3/1/2013        509.5       NULL            NULL            1         
1010-000    3/2/2013        5073.66     V1              2/14/2013           2         
1010-000    3/2/2013        5073.66     V1              2/14/2013           2         
1010-000    3/2/2013        5073.66     V1              2/14/2013           2         
1010-000    3/4/2013        25          NULL            NULL            3         
1010-000    3/5/2013        18          V2              2/18/2013           4         
1010-000    3/5/2013        18          V2              2/18/2013           4         

So how can I get Report Builder to add just once for each ID (resulting in 5626.16)? Thanks in advance!