Probably you can't - and certainly not reliably.
.NET applications need the .NET framework, which is checked and if necessary installed by the installer package. If it is not installed, then your application cannot run. So you need to run the installer first.
However, you could run your application as part of the setup process - a registration component say - which runs before the setup is complete. There are instructions for that here:
http://msdn.microsoft.com/en-us/library/d9k65z2d(VS.80).aspx[
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