I know Blowback Armory sells a 'custom' WE AK47un with a Midwest Kink rail - so I would assume that you have real-steel options that work with little/no modification much like a lot of M4 furniture choices for the WE M4 lines.
http://www.midwestindustriesinc.com/index.cfm?fuseaction=category.display&category_ID=410I would love to own this setup myself - but I've got a lot of work to do on my WE M4 still.

Damn thing never sees the light of day - but looks smexy propped up in the corner of my bedroom with a barrel-mount M203 and crappy Red-dot.
As far as cheaper airsoft rails - I don't know what will fit for certain, but most AEG Aks I've seen/handled still have room for the gas tube and whutnots in the handguard, so I can't imagine having too much trouble fitting one unless the dimensions are just that far off in other areas. (My M203, for example, needed a touch of dremel to accommodate the wider barrel of the WE, compared to the TM-spec AEG outter barrel.)
I'm curious to know what's moving under the handguard on the WE? The real ones dont move in that area do they? And the WE action should all be in the bolt area?
I suppose I'm not really helping as much as adding more questions, huh
Poke Renegade and see if he knows a specific brand Rail with 'lots of room' inside, perhaps?
With all the pretty flowers and twigs in your ghillie.. perhaps you should take up gardening?