I don't think you can do it b/c it requires filtering out the total column. If you could make a list ahead of time of the rows that will be negative, then you could use this to filter the data before it gets to the cross-tab. But to filter rows after the cross-tab has already processed the data is too late.

Sounds like the right way to go about it. People try to do too much with the cross-tab object when a lot of times you are better off cleaning up your data on the server prior to printing it.