I was thinking a router table would work, if you use a straight bit long as the dowel diameter. You just need to use some feather boards to hold the dowel in place against the table and the fence. Drill a square section block at one end to keep it from spinning. Do not remove a full half in one pass, but take several small shallow passes to work up to the final shape. The outfeed fence needs to have a shim that is about the same thickness as what you are removing in that pass. Like you are edge-jointing a panel on the router table. Note that the dowels will probably warp and twist when you cut them as you are releasing stress grown into the wood grain, so I would keep the lengths fairly short, only slightly longer than the final cut needed.

one example for a really large dowel:
http://www.woodworkersjournal.com/f...s-router-table/

http://www.woodworkingtips.com/etips/etip031114wb.html

http://www.finewoodworking.com/2008...gs-featherboard