Get a piece of white masonite and cut a piece from it approximately the size of your press. Lay it on your workbench and stand a full length fiberglass lam on its side(.030 core tuff is very flexible, yet has enough 'spine' to effect bends without flat spots) and place objects, heavy enough they won't slide around, at whatever location necessary to form the side profile that appeals to you. You can use deflex and reflex measurements to guide you if you have some in mind, or just wing it.
To hold the glass in place I've used cans of beans, coffee cans full of nails, chunks of metal, whatever is laying around.
If you have an idea of how much reflex, deflex or whatever you want, you can take measurements up from the bottom of the masonite to locate them... and even if you wing it, such measurements can be taken on each side as you progress to keep them even.
When you get a profile you're happy with, carefully trace it, cut it out, and transfer the profile to the press and cut it out too.
If you use a pencil or dry erase marker on the masonite, you can erase it and redo it until you're happy with it... but really, you can just keep moving the weights around until you get it the way you want... then trace it.
Try it, the possibilities are many, and it puts your ideas out in front of you where you can see them and make adjustments as many times as needed.
I keep all my masonite patterns as a sort of 'catalog' in case I ever need to make a new press, or someone wants to copy it, etc.