I think you could do it with scripting if the gopher server in use
supports some sort of CGI method. Several of the currently maintained
servers do. I think on SDF the Bucktooth server has scripting disabled
for security reasons.
There used to be gopher-to-ftp gateways but I don't know of any active
ones; would be a worthy project!
If you may be able to create simple HTTP-style links in your gophermap
file(s). These generally off-load the means of following the non-gopher
links to 3rd-party apps which are generally called from the client side.
Using a client that understands gopher:http:ftp:usenet such as the Lynx
browser can make the experience appear relatively seemless. Check
the man pages and/or the various tutorials for proper gophermap syntax
when creating HTTP-style entries.
HTH,
Simple Machines