Proclaim does not allow you to specify a custom installation path. However, once installed you can remap where some of Proclaim's data directories are located. If you're looking to save space on the installation drive try moving the MediaCache folder to a separate drive.
- Shut down Proclaim.
- Move the MediaCache directory located in %LOCALAPPDATA%\Proclaim to your other drive
- Open a command prompt and enter the following commands
mklink /J MediaCache <path to new location, e.g. D:\MediaCache>
This will create a symbolic link from where Proclaim expects the MediaCache to be to your other drive.