Hi DSW,

i have been there. 

the way i have handled it is with strapping tape (the kind with glass filaments is best as it does not stretch). 

i take the strapping tape across the hull at multiple locations along the hull and pull the hul back to the right shape and align it with the stitch and glue hulls.   

i then actually attached the deck to the hull (again using strapping tape) to pull it into final position/alignment (note the prior steps tape is still in place).

i then used thickened epoxy to tack the deck to the hull.  when that cured, i then removed the strapping tape that was temporarily holding everyhting in position, and proceeded to complete the hull deck joint per the normal instructions (tape the joint from the outside to prevent epoxy leaks, paint the joints with thickedn epoxy, then glass the joint fom inside, remove temporary tape that was preventing leaks and now do outside joint).

its a bit of extra work, but the temporary taping worked fine and the strapping tape was easily able to handle the pressure leaving my two hands to deal with the now properly aligned hull.

h

   Excellent. Thanks for the help. I'll tape up together and then tack the joint as you describe. Appreciate the advice. David

   And depending upon location/geometry, a ratchet strap or home-made Spanish windlass (one or more) wrapped aroung the whole boat can take up much of the load while getting alignment fine-tuned as you apply the tape. 

Or, geometry dependent, the strap(s) can even be wrapped aroung the deck only if that works better - a strap is only 1/16 th inch thick and can be pulled out of the seam after stitching or  tack welding so long as you are careful not to glue it in place.