First, a disclaimer - 'cause I've never actually done what I'm about to suggest ...
I don't use foundation, never have, and doubt I ever will - but - I
do love a challenge, especially an engineering challenge ...
Maybe it was 2 or perhaps 3 years ago I bought two sheets of plastic foundation to cut-up for an experiment, and so at the same time I also bought two sheets of wax foundation with this specific idea in mind. But I never did get around to trying it out ... but here's the procedure I intended to employ, if anyone's tempted to have a go.
The plastic foundation I purchased had 'proto' cell-walls, and I believe most plastic types have this feature. Wax foundation on the other hand is simply a plain sheet of wax which has 'dimples' embossed into it from both sides by a pair of inter-meshing rollers. So - wax foundation is the right kind to use for what follows ...
Lay the sheet of wax foundation down onto a dead-flat surface, protected by a thin plastic sheet. Construct a 'dam' around the foundation by placing thin battens underneath the plastic sheet, such that when epoxy resin is poured onto the foundation, the resin will be retained within the 'dam'. There will only be a need to fill the dimples within the foundation, plus a millimetre or two above that wax sheet. It will of course be important at that stage to ensure that any air bubbles present are removed.
Once the epoxy resin has set (say overnight), 'butter' one side of a sheet of plywood around 10mm thick with a layer of epoxy putty (epoxy resin mixed with talc or similar) and place this on top of the hardened resin, and again leave to set overnight.
Next day, invert the plywood so that the wax foundation sheet is uppermost, and then repeat the same procedure on the other side.
Eventually you should end-up with a plywood-resin-wax-resin-plywood sandwich, with the wax foundation firmly trapped in the centre. Do not be tempted to split this sandwich apart - just yet.
What you now need to make is a clam-shell holder - think something along the lines of a toasted-sandwich maker. I'd suggest making this from one-inch angle-iron, with a pair of good-quality hinges welded to one side, some means of clamping the bottom frame to the workbench, and with an operating handle attached to the upper frame.
Now this is where it gets tricky. You'll now need to carefully cut away the excess epoxy resin from around the sides of the sandwich, such that the two sheets of plywood with their epoxy impressions of the foundation can be separated, and yet you need to keep them firmly in place for the time being, in order to maintain the precision 'register' between them.
Attach one sheet of plywood to one side of the clam-shell holder, then invert the holder and secure the other. Much easier said than done, this being perhaps the trickiest part of the build. Only when both sheets of plywood are secured should the sandwich then be opened. Hopefully this will be straightforward, with the wax to epoxy interface breaking apart easily - but as I've already said, I've never done this, and so there are no guarantees here.
What you should now have is a clam-shell embossing machine. You'll still need to make thin sheets of wax, as per the excellent 'Way Out West' video, and keep them warm and thus pliable before 'stamping' them into embossed foundation. I also suspect that you'll need to spray or paint washing-up liquid onto the mould surfaces from time to time, to act as a release agent.
Will it work ? Well, in theory it should. (Famous last words ...)

Although - I would prefer to use rollers rather than stamping flat sheets, if that were at all possible ...
LJ