Try creating a calculated field with something like this:
=
Right((Fields!test.Value),
Len(Right((Fields!test.Value),(Len((Fields!test.Value))-Instr((Fields!test.Value),","))))-
Instr(
Right((Fields!test.Value),(Len((Fields!test.Value))-Instr((Fields!test.Value),",")))
,",")
)
This will...