Luggage tag FOB. I like the way you think HelloSailor.
I've looked at the marine man overboard equivalents and disregarded them because of cost and how new they are to the market.
I can raise my hand to your question and I'm also a SCUBA diver. I know damn well exactly how hard I am to see in the water, but I could usually see/hear the boat and the boat I could see didn't even have a mast! There are some interesting tests out there about using a dive boat to locate the diver. They're usually in calm water, and they find that it's damn difficult to find the person in the water.
The dive sausage is a good idea also that I have explored. Why have the rescuer take his eyes off the MOB in order to launch a MOB pole that the victime may not even be able to get to? Wouldn't it be much better for the victim to already have his own inflatable MOB pole? YES!
In the SCUBA world they're called Surface Marker Buoys or SMBs. They're great because they give you height and movement. Height you need to even be in the field of vision of the observer when you're bobbing amongs the waves, and movement attracts the eye. They also make a fine place to hang your strobe and often come with reflective tape. Another plus, is that they provide you with extra boyancy.
This one from the brand XS is the smallest, mouth inflatable (many use your scuba tank) most compact, and best unit I could find when I did my research.
Buy XS Scuba saftey sausage AC190 with reviews at scuba.com
BTW I also like your idea of using a waterproof radio bag over your waterproof VHF. Good belts and suspenders approach. Another option is to buy a VHF designed for scuba diving and rated to 425ft depth. I mentioned it here on SailNet a while back. Technology can aid safety....
It has DSC also. Actually, now it looks like they're marketing it to sailors as well. Nice to get a nod from them.....