Any way to change default extension for a platform?

[Masamune3210]

I keep all my games compressed as iso.gz files since PCSX2 can handle them, and it helps cut down on space needed, but when I try to import them Launchbox sees the .gz and picks that as the extension, leaving the iso in the filename which screws up metadata matching. 

Is there any way to change the detected extension, or am I just stuck manually removing the .iso from the game titles