Hi Wez-
Take a look here: http://www.exrx.net/Lists/ExList/WaistWt.html#anchor172895
Check out the cable-based exercises- you should be able to do these. Or, invest in a few plates just for abs- maybe one each 5, 10, 25, 35, and 45lb plates should do it so you can do weighted crunches.
Jake