An elegant solution to this problem is the environment variable TNS_ADMIN. In Windows you can set environment variables by following these steps:
Right click on My Computer
Click on Properties
Click on Advanced tab
Click on Environment variables button.
You can set a new System environment variable called TNS_ADMIN and give the value as a common directory which will contain tnsnames.ora file. For example TNS_ADMIN=c:\tns
Once you set this variable, irrespective of the Oracle client being used, c:\tns\tnsnames.ora will be the single tnsnames.ora file used to resolve oracle names.