I do this with a friend in 10 ball:
We play by-the-game, no sets etc....winner break. It's real cheap.....
I give him first break and 7-out.
If he wins that game, spot is adjusted to 8-out.
If he wins that game spot is last 2.
If he wins that game we play even until he loses a game.
After he loses a game the spot starts over at 7-out.
If I win that game, he gets 6-out.
If i win that game he gets 5-out...... etc..... etc....
Once I lose a game the spot ball spot goes up.....
Works very well and keeps the game even.
Hardest part is determining the starting point.
If it's truly a friendly match for cheap it shouldn't matter if you have to give up the nuts at first until the fair spot is found with adjustment.
Also, you mentioned that you didn't want the sets to get to long....... another reason to do the above.
Btw, what is the usual score in the races to 5 when giving him the 6/break?
Rake
Most days we wind up having sets of 5 to 3 in both directions or hill hill.