FP Ext. will not install - syntax error in value of "xuser" parameter.

I am still not able to install the extensions as the Unix User starts
with a number:

Error:
Value "4waterfi" is incorrect.
Syntax error in value of "xuser" parameter.
Value "4waterfi" is incorrect.
Syntax error in value of "xgroup" parameter.

This is on apache version 2.0.52