as far as i am aware youre in apickle as there is no converion for the wtb hubs, the only converitable hubs I know of are hadley, certain aton lab, halo, and bombshell, also the hopes are typicaly switch-ably.
But what fork are you using if it is a manitou nixon or sherman, they are real easy to swap the lowers on. if it is call adrenaline they'll get you set-up
Sun-ringle has a 20mm to QR plugs that you can use. Atlesat that's what their site says. Go check out Sun-Ringle's website and see in the accessories section I think. I might pickup a pair and try them out.
But no, I haven't ever seen any 20mm to QR adapters besides these. A few companies make a 20mm hub that converts to QR and some basic parts and such which is nice but I've always stuck with Marzocchi 20mm hubs because they're cheap and really good quality. The Sun-Ringle adapters look like the only thing out there to make a 20mm hub QR.