Actually I didn't! I found out that I might be able to do a seperate project and then run this after the normal installation, but didn't find anything more sophisticated... I thought it might have something that you were able to add as a property!
However I then changed the installation method to InstallShild 9, which offers quite a lot of functionality, and actually a bit more than I need! I had to learn InstallShield from scratch, which I then did. I managed to make it work as I wanted, eventhough there is differen things that you have to take into account when adding paths to the environment variable!
Do you ask because you have the answer, in which case I am still interested, or because you would like the answer, in which case I cannot give it to you since I did not find it?!