Use NSMB to update you to 4.1 and provide you with a few new IOS, WFP will surely work then.
We do know that WFP uses IOS53 but we haven't documented it's update as of yet. Most games released in the last few months have been 3.4 updates, apart from NSMB and a few Jap games which have had 4.1. In due course more games will filter through with 4.1 or even 4.2 but that hasn't happened yet.
WFP works fine on my 4.0E Wii, with latest IOS 38, 53, 55 and cISO249rev14 installed.