As a matter of proof of concept and before going deeper with Warbonds as you intented: 1 wbonds per 10 IPCs income.
Play warbonds as a single bonus dice roll for either:
1-order of play,
2-Tech roll,
3-Recover lost unit(s)
Simply use 1 dice, D6 (for 1942 or AA50) D10 (for G40), to try the option about order of play.
Before a given round begin, all powers decide if they invest their single dice in either option 1, option 2 or option 3.
The only exception is the first round of play, because a lot of balance of game and opening strategies are based on turn order OOB sequence.
Suppose it is G40, you have three Allies who want to play before Germany and Italian too. All three allies and Italy rolls, and are put in order of sequence according to the roll. If an Allies roll above its OOB order, nothing happen. If he rolls below, for instance rolling a “2” means playing before Russia. If Italy rolls a “2” or “1”, he would play before Russia.
2- As OOB D6 Tech roll, 1 to 5, nothing happen. “6” means a Tech has been developed.
Of course, you can roll more dice if you pay 5 IPCs each, as OOB rule.
3- Roll D6 for recovery: you can replace lost unit(s) according to the value on the dice.
A given unit have to be taken as casualty in the preceding game round.
1 or 2, there is no unit at 1 or 2 IPCs, so no recovery.
3: 1 Infantry
4: 1 MI, 1 Art or 1 Infantry
5: 1 AAA, 1 MI, 1 Art or 1 Infantry
6: Tank, AAA, MI, Art or 2 Infantries
And any recovered unit can immediately be placed on board in IC during repair phase (if a given IC is too damaged, you can repaired it before placing this unit).