Are there any PL to EF adapters that dont require modification of the camera body, and don't use any additional glass?

Yes there are. KCWtechnica is one.

Shop PL Mount to Canon EOS, 7D 5D Mark II Adapter - V1A | KCW technica (http://kcwtechnica.com/shop/pl-mount-to-canon-eos-7d-5d-mark-ii)

Very interesting! I was going to ask how their's manages to work while no one else has made one for the DSLRs, but it looks like the answer is that it only works on some, mostly older, PL mount lenses. Which isn't a bad thing since that's what I'm looking at buying.