Good idea, but how would you add that into negotiations? It'd be near on impossible.
I am not sure how racing contracts work but in other sports contracts are usually based on the following:
1. Money over set upon agreed time frame (long term contracts usually means lower yearly payments & short term contracts are more costly due to less risk) Player dependent.
2. Signing bonus - Flat fee for signing with the team could be used to have a player sign if agreed contract matches other offers.
3. In season bonuses - Agreed based off set amount of results (finishing in certain positions, scoring title, points etc...)
So I am guessing what would happen in the above idea would be season bonuses (Championship, wins, podiums & points) would be offered in a percentage base say nothing under X percentage should be given.
So while you could pay driver and staff less then X percentage then you would damage their morale but anything over X percentage would see an increase in their morale.
I would also say that if should be allowed to go over 100% since you may have extra cash in the bank that you want to spend for a morale or performance increase.
Other Option would be to remove bonuses outright from negoications and have them set weekly as set above from either 0% to 150% towards staff & drivers.
But either way I really like the idea but would also like to see morale moved to a number based system ranging from 0 to 150 as well to see if the staff member is angry to extremely happy or somewhere in between.