i don't think it’s gonna work, my tip, chuck that ham roller crap in the bin and buy a real mans’ crank set!
whilst the isis is a good bb for road bikes and mid level non bmx completes, its sh*t for flat/bmx cos once you get a crankset that uses the isis bb, then you are stuck with it, the best you can do is get a ti isis bb. all this means you can’t have a million mods (like a different spinal or plastic bb) and we know how much ground riders love to mod. the issues you noted are spot on.
st martin should have never used it (and the only did for a year or two), i'm guessing the reason they did use it was 'cos the rights to it exist in the public domain and they would have got it cheap, rather than pay royalties for a design that isn’t say - crap!
take a look at the link below, it’s related to changing the bearings in an isis drive but it also illustrates your problem.
http://www.amclassic.com/pdfs/ISIS_Overhaul.pdf