Add domain user to local group via web application running under local admin account

I'm trying to use System.DirectoryServices to add a domain user to a
local group via a web application which runs under the identity of a
local admin account. Is this possible?

I can successfully add domain users if I run the application under the
identity of a domain account with administrative privileges on the
local machine (or use windows auth with impersonation), but if I try to
run it under a local account rather than a domain account I get a
permissions error.

Thanks,
Chad Dressler
DIGOP