My pedestal-style CP works pretty well for me, standing in front of my PC monitor. (at least until I put it in front of my actual tv / stereo / everything)
Here's what I'm thinking... If you splice wires with your IPAC using either solder or those wire-splicing ties that slip on over the insulation, cut it, and contact the wire, then you can add two Molex plugs to the ipac inputs, to cover all the inputs for two-player games. That'd give you the same wiring setup as hooking two switches to one Ipac pin, except you'd just plug in the molex from your podium CP and make it automatic and swappable.
Then, leave the back of your podium open, and your original cab's coin door can just sit open, swinging partway into the open back of your new box, allowing you to run a cable with your new CP's molex plugs into the opening. I think you could easily get your new CP thin enough that you'd only be eight inches or so farther back from your screen, especially since you're building an add-on and not a dedicated CP that's supposed to wow people on sight.

From there the only problem I can see is how to keep the new thing from tipping over, since it's going to be pretty thin front-to-back. You could try taping free weights to the bottom of it and maybe that'd work, but you could also take advantage of your coin door being open to hook bungee cords between hooks on the inside of your CP, and the metal corners of the coin door opening. That should attach your panel firmly to the old machine, without marring any surfaces that you care about. You could even try and make padded grooves for the T-molding on the old machine to fit into, keeping it from moving side to side. The bungee cords could be attached and detached by reaching through the addon panel's coin door.