You can get adapters to allow you to convert your backplate and wing setup to independant twins and/or single cylinder.
This screws on through the normal bolt holes on your back plate and allows two cylinders of any size (including 18's) to be used. You can also use it to mount a single to your backplate.
Narked at 60 - Technical Dive Products – Kit that keeps up!
I have a spare one if your intrested, as I am now on a YBOD. PM if your intrested.