I read in some guide that right clicking would do this, but the usual command for right click (Ctrl+Mousepad) doesn't work within the game. This is the free GoG version, which seems to be using ScummVM tho not really.

In ScummVM it's supposed to be command+click to right click. Unfortunately, I just tried this on my iMac with BaSS and it didn't work though (I am running the game using the full version of ScummVM, not the one bundled with the game). You could give it a shot though.

You could also try going to your computer's System Preferences and turning on two-finger secondary click for the trackpad, then try that.

Otherwise I don't have other ideas, if no-one else can come up with a solution I would recommend you try contacting GOG Support.

(I normally use a mouse with my iMac, and the normal secondary click (right click) works fine in BaSS, it's only when I try to use control+click or command+click that it doesn't work).