Unfortunately, there is not a way to do that in ACT!. There may be a third party add-on product that can do this such as Durkin Opportunity List Plus or Product Pivot.
If you like to see this feature added to ACT! in an update or future release you can submit a Feature Request or post your idea on the Share Your Ideas board on this Community.
Greig HollisterNote: Effective 6/1/13, Sage no longers provides support for the Act! software. This is now provided by Swiftpage.