I was going to post this, but managed to dig up the answer, so here it is in case anyone else is looking...
My app installs a windows service via:
string[] installargs = new string[] { binaryname };
ManagedInstallerClass.InstallHelper(installargs);
However on a 64-bit platform I want to force the installation to use the 64-bit installer (the equivalent of the Framework64/InstallUtil)
How do I get ManagedInstallerClass.InstallHelper to run the 64-bit version?