I know this post is a couple months old, but I'm a solo gamer and I'm thinking about getting WaW 85 so this is a question for me too. I have a couple ideas based on what I've seen of it and from the expansions description. The hidden aspect of deployment would have to be "simulated" if you will. As a matter of fact the the opposing sides actions and deployments in general likely are going to have to be simulated (as in not actually played out, in contrast to how the SOLO system works). Any solo system (that isn't you making decisions for the opposing side) for this is going to alter the way it plays quite a bit from the original two player experience. Again I don't have the game so I can only offer concepts not specifics.
You wouldn't actually track the deployment or forces of the opposing side. The makeup and "movement" of their forces would have to be dictated from a set of rules or a chart of some kind, and there would have to be new rules for how to handle recon. It would of course involve a certain degree of randomness (perhaps a set of goals could offer direction), but I'm sure a dedicated solo player could come up with a set of at least basic house rules to give it a try if they wanted.
Alternatively you could just throw the hidden aspect out all together and have the opposing sides moves actually played out, but I think having that hidden aspect would be more fun.