Thanks for all the tips. Y'all sound pretty ambivalent so I probably won't do it.
Respacing the Hugi hub to 135mm looks possible, having partially disassembled it, but it looks like it would require access to metalworking tools both to cut down the axle and to cut/grind down parts of the pieces of metal that go on the axle.
http://www.dtswiss.com/Resources/200...D_ED_2004.aspx is the tech manual for the hub. It appears the specific model I have is "HR / RW Hügi Tandem Arai 140mm". It would perhaps be possible to remove/modify "Aluminium disc 140/145mm" and "RW adapter (right), complete" in addition to the axle, but that'd be quite a task.