If you make a mouse input, it should show the control scheme including the mouse, which has, if i recall correctly, boost on rightclick.
I'll check if there are any config files to change keybindings or if it's hardcoded once I have the time later this week

For the record: there doesn't seem to be a way to rebind the controls.
Though: the game displays the controls fitting to the last button press, so, my previous comment may still help.

Depending on your system software, there should be a way to rebind any key outside the game to 'create' a virtual right ctrl key.