eRC Micro Series 2.4 GHz

It appears to be a uni-directional binding from your image, which implies it can be implemented reasonably easily. But on the other hand, it does not appear to have a huge following. I'm not sure how many folks are out there who would have these models and also own Walkera Tx.

Easy is one thing, but I need the equipment in hand, and for me to spend $60-$80 (plus shipping) there needs to be some return on investment. I already have a backlog of Protocols to investigate. I figured there was at least some overlap between folks interested in the HubsanX4 and those who have a Walkera Tx, so I went ahead and implemented it (plus the X4 is a pretty cool UFO for me to fly). But folks who own a Walkera Tx are much less likely to own planes than multiple helis, and in this case, it may well be just you Also I don't have the space to fly planes, so there isn't too much personal incentive.
If you ever see any tx/rx for sale cheap (maybe someone broke their plane beyond repair) let me know.