That is definitely one option I was thinking of. The only thing I don't like about that idea - and it's minor - is the time it would take to deflate and stow it at the end of the dive, as you're starting/going up. Also, it would be potentially more drag than a smaller float. Meaning, if there was nothing to tie the leash off and I took, say, a lead weight down to anchor the strobe, a stiff current could pull on that SMB and drag the whole thing away.
Another option was a non-compressible float. I.e. a high-density foam thing. Maybe sized to be just a little more buoyant than the negative buoyancy of the strobe itself. I was thinking that would likely be pretty compact.
For the kinds of dives I have experienced where this setup would be useful, being able to quickly deploy it and clean up and stow it are somewhat important. Some of these dives would be NDL dives. Spending 5 minutes screwing with deploy and stow out of a 25 minute NDL would be non-ideal.