Warmane Without New 3.3.5a install?

So I've been playing another private server recently(Project Ascension), and I got the craving for a more typical Wrath experience. I figured since PA doesn't actually use the realmlist and instead does things through its own custom .exe, I could set the realmlist for Warmane, then run the game through Wow.exe and it'd work out fine. This thought process was further spurred by the fact that previously I got PA working by just dropping its .exe into a normal 3.3.5a install set to play on Warmane and could freely switch between the two based on which .exe I ran.

But apparently my assumption was erroneous, because whenever I try to play Warmane like this, the game crashes before it fully loads and I get the error message "Your login interface files are corrupt. Please reinstall the game."

Does anyone know of a way to get things working the way I was originally planning? I'm at a point with my data cap this month where I'm not wholly comfortable downloading another 18GB.