the following is just "my guess":
in a testing environment, i was able to install rs in a web server as presentation layer, and then its db in a separate server.
now, the web server was stand alone, and sql server was part of a domain.
the setup was w2k sp4, iis 5.0, sql2k sp3a and .net framework 1.1. (at that point in time there was no sp for .net framework 1.1).
now, my point is that the aspnet account, from this stand-alone web server, was doing pass-thru authentication to this sql server and another file server in this virtual network. well, my solution is an accident from a previous setup. actually, it looks to me that before trying that, you should make aspnet account, from your dev maschine run as a network service account. this is thinking security is not an issue. my solution requires creating aspnet account on sql server with minimal privileges. actually, this worked fine for me for a file server, where i made it a regular user with full share permissions over a shared folder.
please, let me know if your solution is anyhow related to this. i might be doing setups like this in the near future.
"What you think doesn't matter. What matters is evidence..."