i was thinking about this today , and if you have a couple around , and youre not planing on using them , why not plane down two sides , glue 3 or 4 (or 6 for hex shafts) together , then plane all the excess off , back to round.
check spine along the way.
you could also make yourself some short-draw arra's at 20" or so. i hear major shortening makes up for low spine.
and dont worry , i havent cut my bunny killers down yet , they are still mostly 36". shot through em yesterday , and compared to the 3/8 dowels , these things are like tiny darts . i may or may not shorten them up...
-hov