So I have a Bagster/Baglux tank cover on the R1200GS and a tank bag to hold my laptop which clips in nicely to the tank cover. Really I only need the bag on the tank when I'm carrying a pillion so it would be really useful to clip the bag on the back of the bike for the commute.

Is there anything available that I could mount to the back of the bike to clip the back on there? (Besides just using bungees or straps)