A few years ago at my last job...
     We had some "quick and dirty" fixtures for some .028 flex assemblies 
     made at a local board shop.  We gave them a penciled sketch and they 
     worked some magic with their Excellon.  They used.093 unclad FR-4 
     material. They routed the board shape ~.030 deep, and routed thru 
     where the thru hole parts needed to contact the wave.  We allowed 
     ~.050 gap between the edge of the pads to be soldered and the edge of 
     the openings.
     They also made some FR-4 "clamps" with slots for stainless steel #4-40 
     fasteners.  The assemblers dropped the board in, slid the clamps over, 
     and installed the thru-hole parts while standing right there at the 
     wave solder machine.
     The assemblers ran them 150-200 passes over the wave, and they still 
     looked new when the project was complete. (We learned later that the 
     assemblers were weighting the boards in the center to keep the wave 
     from pushing the board up and allowing the solder in.)
     
     Joe.