In photo 5 of 10 in the gallery link, there's an interior shot with a detail I hadn't noticed before:
Attached to the driver's side, there's a leather holster-looking appendage that might be used to hold a bottle, or ...?
Steve, I don't think you're correct in your assumption. I'd suggest that is to hold the Nitrous Oxide Systems bottle (for when you want extra umph!). Morgan have already solved the problem you speak of with this optional extra...
AsboJohn can be seen modelling it in this photo (he does some fashion work in his spare time but is very modest and never mentions it).