I’ve had major issues setting up RPC/HTTP against my new e-mail hosting service. First of all Outlook 2007 with sp2 won’t let you add an account over rpc/http. You have to be local on the domain. This is not possible with a hosting service.
After a lot of back and forth I came up with the following solution. I had the hosting provider set up my account on a machine at their location. Then export the HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows Messaging Subsystem\Profiles\<profile name> key from registry. I then edited the reg file to point to an .ost file on my local machine, fired up Outlook and it all worked :)
It requires a bit of registry knowledge to do this, but it shouldn’t be very hard making a program creating a correct MAPI profile for any user with the correct data.