It's possible to back door the server but unless you wish to spend your time learning to brute force or use hydra then i'm sure its not worth the troubles. Because if your only after noclip and not a full set of admin controls then a backdoor is but isn't what you're after, I have a backdoor script which allows the SteamID inserted into the script to be put in the desired group specified e.g. superadmin, which has got noclip but yeah.. Yabbering on atm, Main point, Unless your willing to backdoor a server then i'm not aware of any other ways