I just got done dealing with this problem and it's very fussy even on a flapped airplane, at least if you aren't willing to cut access holes, which I try to avoid at all costs.
I hadn't really thought about it too much for a built-up fuse unflapped airplane. You either have to build the formers and leave sufficient clearance to slide the pushrod all the way to the back through the wing cut-out, or do like they used to and the way it is shown on the Nobler plans - build the fuselage around the pushrod. I don't like access holes through the fuselage, at least not with IC engines, too much loss of rigidity, and also prone to fatigue at the corners like a DeHavilland Comet.
For the wing cutout method, i would be tempted to make the diagonal cuts to remove the bottom of the fuselage sloping towards the front rather than the back. that makes it easier to get the leading edge in without having the pushrod go in at a large angle.
I haven't built the formers as solid parts in a long time, all of my formers are built-up and have capacious openings in the middle. They are built from 1/16x3/8 strip with overlaps at the corners. They are also have diagonal braces on the top and bottom edges. I think Sparky posted a picture of my crashed airplane from the 2005 NATs where you could see it. Also on Jim Aron's airplane, after he crashed that, both are posted somewhere.
Brett