Wrong host in HTTP post on test pages behind reverse proxy

[stigip]

I'm having a problem with hosting a web service on a server behind a
reverse proxy. When the IIS/.Net Framework is generating the test page
for a WebMethod in the .asmx-file it uses an absolute path in the HTTP
post of the invoke-button. This poses a problem because the internal
host is not known to the public. Is it possible to instruct the .Net
framework to use either relative paths without the host or a specific
hard-coded host (i.e. in the web.config or elsewhere)?

Thanks,
Stig Irming-Pedersen