I'll expound a bit - I'm the friend in question.
I'm well familiar with the backpressure issue (although more theoretically than in practice - in fact my bike runs like the dickens with wide open pipes), but it's not the problem I'm trying to solve. This thing is loud - not loud like midlife crisis loud - loud like Germans invading Poland loud. Trouble is, I've moved to a lovely town full of hippies, yoga classes, farmer's markets... I wouldn't make it half a mile before I was beaten with daisies and hung by hemp rope from the nearest tree.
So here are my thoughts: 8" universal baffles would fit in the end of these pipes - I could wrap with glass and hope for the best, but how much of an effect can I expect this to have? Alternatively, I'd love to have some pipes made to extend from my tt's up and around my rear tire at 30' or so to which I could mount some proper (albeit short) mufflers. Any pipe builders in the community? I'm comfortable doing most mechanical work myself, but metal fabricator I'm not.