Nick beat me to the tritone sub. You can play C#7 -> B7 instead of G7->F7.
You could also do some lydian dominat stuff. Basically just throw in a #11. Try coupling triads with the lydian tonality. That means you can play G major and A major triads over the G7 and F major and G major triads over the F7.
Altered scales are the other relatively easy alteration. Play Ab jazz minor over G7 and F# jazz minor over F7.
That should keep you busy for a while.
