I don't know about tricks for freewheels, but generally speaking BB tools slip out of the cups too, here's a tip for that:
Take a crank retention bolt to your local DIY store, and ask for a 1 inch long version (so, same threadcount and diameter) and some washers. Put on the BB tool, then use your new bolt and washers to hold it inside the BB cup as if it were a crank, whilst you tighten.
I don't know about tricks for freewheels, but generally speaking BB tools slip out of the cups too, here's a tip for that:
Take a crank retention bolt to your local DIY store, and ask for a 1 inch long version (so, same threadcount and diameter) and some washers. Put on the BB tool, then use your new bolt and washers to hold it inside the BB cup as if it were a crank, whilst you tighten.