I just had the most awesome idea... at least I think it is, and theres a good chance it already exists, so please don't flame me!! lol.
With cruise control on a manual, I remember someone once saying something about cruise going off its nut on the throttle when you change gears with it on...
The solution to this problem would be to connect a normally closed style switch to the clutch pedal (similar to the cruise cancel switch on the brake pedal) and connect this in parallel with the 'coast' button on the indicator stalk!!
So heres the chain of events...
Guy presses resume on cruise while he's doing 60 and in 4th gear...
Cruise accelerates up to 80 and guy presses clutch...
when guy presses clutch, switch returns to its normal 'closed' position and 'coast' button is pressed, preventing cruise from accelerating.
Guy is now in 4th and lets clutch out, which unpresses switch.
Cruise now resumes at the speed car is now travelling...
God I hope this doesnt already exist lol because I would feel really smart if its an original idea