Step 1: Get an item that can cast wish.
Step 2: Trap yourself in a zone of silence. Arrange it so you can get out without spending an action, but only with a good roll; say a 20. Failing should not do damage, just return you back into the trap.
Step 3: Create a Simulacrum or other "sacrificial" being (like another party member) to use the wish item.
Step 4: Repeatedly try to get out of the silence trap. When you do, immediately cast wish using a spell slot.
Step 5: If you suffer blowback, the Simulacrum wishes a reroll of your escape of the trap, with disadvantage.
If you fail to get out of the trap, you could not have cast wish, so you could not have suffered blowback.
If you require a natural 20 to get out of the trap, then the wish'd reroll has a 1/400 chance of getting out of the trap.
While in the trap, you cannot cast wish, as you are silenced.
So, you are basically immune to blowback.
Using multiple wish-casting items reduces the chance by a factor of 400 for each additional one.
This makes it take an average of 20 rounds to cast Wish, but a 1 in 1200 chance of blowback sure makes it worth it.
Note that you can generate a more complex system. For example, arrange it so that person B has to first escape (rolling a 20), which gives person A a chance to escape (also rolling a 20). If and only if both escape then person A casts wish.
If A gets blowback, then person B wishes a reroll.
If person B gets blowback, then sacrificial wisher C (simulacrum, other party member, etc) with a wish granting magic item wishes B rerolls, or if B's reroll of A doesn't work, C also wishes B to reroll their escape.
After an average of 400 rounds, A and B escape.
Then A casts wish. 67% chance everything is fine. 33% chance of blowback.
If blowback, B casts wish. 67%*399/400 chance we have recovered and can try again tomorrow. 67%/400 chance C has to force B to reroll, with a 33% C blowback, 67% success, and 399/400 that everything is undone.
33% chance B has blowback (and either A failed or not). Then C wishes and has a 33% blowback, plus a 399/400 chance to undo both A and B's wishes.
So 33%*(33%+67%/400)*33% C (item holder) can never wish again, aka 3.63%.
33%*(33%+67%/400) chance to burn a charge on the item (aka 10.9%).
The chance that either A can never wish again is 33%/400^2 or about 1 in half a million.
For B to never wish again, A must first fail (33%), then B must fail (33%) then reroll must fail (1/400) for about 1 in 3600 chance.
If you have N wish casters and 1 sacrificial item holder, the first N-1 wish casters have a 1 in half a million or lower chance of never casting wish again.
The last one has about a 1 in 3^N*400 chance of never casting wish again.
The number of rounds it takes everyone to get out is 20^N. This will get ridiculous pretty quickly.
The trap requires all previous people exit before the next one can even try; so the trap complexity gets pretty insane pretty fast.