You're a genius Boznoz. That's the trick. Thank youfind someone local that owns a 3d printer and just print an attachment , cheapest and fastest solution.
or you can get any of the gopro mount extension accessories and glue / screw it / zip tie it somewhere for a temp solution.
EDIT: I am checking the Elgato , is there a tripod mount holding that phone grip? you could just unscrew it and use any aftermarket gopro tripod mount like this one
GoPro Tripod Mount