What you show in your first post is exactly what is used for boost tabs. However, the boost tabs need to be limited to 10% or less of the moveable surface else severe hunting occurs when you are near neautral position. This is used quite often in many of the larger models, both on elevator and aileron as the servo load is reduced a great deal permiting weaker servos to fly large planes. I frequently use this on some of my bigger planes and on the quarter scale Facetmobile to allow 30 inch/oz dervos to replace the 100 inch/oz ones. I am told that Burt Rutan used this same principle to show that our little 30 inch/oz servos could fly one of his full scale canards by flying the boost tab on ailerons with electronic control (an RC servo only) and no other input.