It used to be possible to make sub size 1 missiles and fill a missile with multiple submunitions which were nothing but an engine, they has good potential as decoys against AMMs.
I seem to recall that it's not possible right now, but i could be wrong.
Still you could make an amm carrying missile which has the same size, speed and range as your standard ASM. Set the bus to drop the AMM version just before the missile gets into your enemy's AMM range.
Just a quick analysis of how effective this might be using full size 1 AMMs.
Say you would normally launch a salvo of 12 size 6 ASMs, the enemy manages to intercept 50% leaving 6 to hit, perhaps one misses (16.67% miss rate) leaving 5 hits.
If you replace half your ASM's with the decoy variant you would need double the hit rate to make up for it.
The effectiveness of this strategy depends on a few factors, but mostly on interception rate and number of AMM salvos. Let's say the AMMs get 2 launches against the ASMSs. The last example had 50% interception so lets say 29.3% are intercepted per round. (times 2 rounds leaves about 50% of original missiles surviving.
Now launch 6 size 6 ASMS and 6 size 6 Decoy ASMS.
We'll assume that the enemy targets the ASMs with half it's AMM launchers, and targets the Decoy Buses with the other half, while the submunitions should have launched already, they probably won't have been targeted.
2-3 ASMs should have been shot down, and 2-3 Decoys should have been shot down, however the next round now faces 3-4 AMM decoy buses, and their submunitions, if the decoys were only 1/3 submunitions then you would have 6-8 decoys inbound.
Now rather than loosing an additional 2 missiles and having only 6 remaining, you'll find that there's now double as many contacts for the enemy to target, so the survival rate against the next wave is doubled. The end result might be 60% of missiles surviving to hit. Half your missiles would be full ASMs and therefore from those you make 60% of your original damage, in order to have any positive effect then your AMMs would need to produce 40% the damage as your ASMs.However since your AMMs are 16% the size of your ASMs then it's likely they would only be doing 16% of the damage.
So it doesn't look good, however if all the decoy buses manage to unload their decoys before being intercepted, and each attempt at interception gets divided amongst all missiles including the submunitions then it looks rather more effective, but i'm too tired right now to calculate this.