I did Canaries to Barbados in 2003. We left La Gomera in mid-November, which was earlier than recommended, because of crew constraints. The trades hadn't fully settled in and we had a few stretches of light winds in the early part of the trip. Since it's now mid-December the trades should be getting more reliable. I'm not familiar with the boat, but if he has an inner forestay he could wing out a staysail to windward, with the genoa on the leeward side. If nothing else I'd probably try the rig and see how it steers and handles before motoring all the way back.

(edit) That said, I wouldn't underestimate the length of the passage (it took us 22 days due to the light winds early on) or the potential bounciness and rolling once he gets into the trades. If he doesn't have a mainsail to help provide stability downwind maybe the rolling would be aggravated - especially if he only has one pole and can't get the sail control of a true double-pole wing and wing or "butterfly rig" as a Dutch single-hander we talked to on the passage so appropriately called it.