Oracle Database Discussions

Hi,
I have an objective. I want to have two tnsnames files. One in the network drive and another one locally. I want to use the tnsnames file in the network drive, if not available then use the local one. I was able to acheive this using TNS_ADMIN environment variable. Could I do the same thing using ifiles also? If yes, how can I do it?
I was reading about ifiles in the documentation. But I don't know how to use this in this above context. I thought by doing small things like this I could get a better grip of the ifile concept. If anyone had done this already please let me know.

Thank you,