Nice idea but no easy access at the fuel stations,once the leathers are on that's it for the ride so maybe just another better design bumbag like bootsam's post
or a money belt, would fit under leather. https://www.rohan.co.uk/Eagle-Creek..._w9dIx-y1HXnJSlfVQRoCKCUQAvD_BwE&gclsrc=aw.ds
neck wallet: https://www.rohan.co.uk/Eagle-Creek...Wallet?ocode=04173456&relatedType=Alternative (don't come crying to me if you decapitate yourself)
I assume your leathers are for highest safety. So why compromise them with risk of organ damage from bumbag contents?