Sorry, to clarify, I have both a flight stick (an old Saitek Cyborg 3D gold) and an Xbox controller. I mainly use the stick, but haven't bothered sorting out stick bindings for the SRV, because it's a pain to do, and I like how it works with the Xbox controller in any case.
But currently, the Xbox controller doesn't just work, I have to go into the menu and select it whenever I get into the SRV, and then back again when I want to fly off.
The custom bindings file looks like it's just some kind of XML, so I guess I could copy in the relevant lines for the Xbox controller - if I could find them. I could also manually bind all the Xbox controls in my custom flight stick bindings, but I feel there's an easier way.