You could try jdeGetEnvironmentPaths. It definitely works on the client and probably works on the server.
You can search the source directory for examples (search b9*.c).
One example of its use is in the B9800380:
jdeGetEnvironmentPaths(hUser, szEnvironment, szPathCode, szSysPath, szAppPath, NULL, NULL, NULL, FULLPATH)
in the above call you pass in a valid hUser, szEnvironment, and szPath code. The API then populates the szSysPath and szAppPath with the path strings. So if you pass in DV7333 for szPathCode and szEnvironment, then szAppPath will have the c:\b7\DV7333 path.
Give it a try and post back if it works on the server.
Good luck.