How to run setup.exe as a 64 bit process

I need to call a dll custom action from Basic msi project.I have converted the Basic msi project to support 64 bit installation, but the setup.exe is running as 32 bit process. Now that the dll project is converted to 64 bit, I am getting an exception of msiexec.exe when I run the setup.exe. When I changed back the dll to 32 bit, there is no error. Is there a way to run the setup.exe as a 64 Bit process?
I am using Install Shield 2012 Spring Edition.

Regards,
SG