I'd recommend giving Shaikh a call over at FCM and asking him about this. He will be happy to help and is extremely knowledgable when it comes to suspension setup.
While I'm not expert on the MS3 setup it sounds to me like the bumpstop that you would get from FCM is going to be stiffer than the stock unit. On top of that MCU bumpstops are much better than the rubber ones that you will be replacing.
I did contact him already and he basically said get a strong zip tie and it should hold it in place....I was like SERIOUSLY???? so I already removed them and cut the stockers and put those back....car already rides a bit bumpy so no reason to have even stiffer stops in ...
