You did not specify the software, but one possible workaround is to bypass the installer by installing the software on 32-bit machine and then copying installed files to your 64-bit system and creating necessary registry entries manually. (You can sniff them by Process Monitor during the installation. See comment below for helper PowerShell scripts.)
This could be very labor-intensive way for complex applications, but on the other way, there are many applications which use the installer simply for copying the files, creating Start Menu items, writing few registry entries (if any) and nearly nothing else. In such cases, you could easily succeed.
Another thing is whether the application would be able to work properly in 64-bit environment. You can try with compatibility settings and you might or might not succeed. But you asked for a workaround so here it is.
Another attempt to open the installer package manually (in many cases it is either executable ZIP file or Windows Installer package) and extract its content. MSI installers and some EXE installers can be unpacked this way although you will basically get the same file set which you get on 32-bit machine, so no big deal here. But in many cases such an extraction is possible.
Related links: Unpacking MSI package and Opening self-extracting EXE archive.