Here is my recurve form... It was easy because it comes in 1.75" thick and that is what I needed...
Here is my one piece longbow form... It was too wide to run in my planer 12.5" planer so after I cut the basic shape, I than ran each piece in the planer to get it down to 1.5"
Here is my T/D longbow form... I did the same thing to thin down this form to 1.5"
I dont know if this would work, but I have often thought about taking a router and setting the depth of cut to 1/8" and then taking 1/8" off each side just around where the bow would touch the form on each side... you would then habe a form that is 1- 3/4" thick but only 1.5" thick where you need it...