[Wine] dll override for select apps only

[Thor]

I've been experimenting with Wine on Ubuntu Edgy.
I installed WinRAR, and when it didn't work, I looked at this page:
http://frankscorner.org/index.php?p=winrar350
First I copied the required dll (comctl32.dll) over from Windows to the 
program dir (not the Wine windows dir), then tried to add it via winecfg, 
simply entering the name in the dialog.
Then Winecfg couldn't start again.
I then followed the terminal instructions instead: 
WINEDLLOVERRIDES="comctl=n" wine winrar.exe
and now WinRAR worked. But other programs that did work now don't, including 
winecfg, complaining about the dll dll I copied over and put in winecfg.

Editing user.reg to remove the reference to the dll, winecfg and apps like 
IrfanView now work again, but WinRAR doesn't.

How do you override DLLs on an app-specific level?