I would somehow cover the hole for the cable release in the shutter button. A softie or piece of cloth tape should do the trick. I don't think there is much you can do beyond that, unless you start to wrap the camera in tape. Just be judicious in how much the camera gets exposed. Carrying a small cloth is a good idea.
Just last week I was shooting at an event in the poring down rain with my M6ttl, M7 and a Nikon F2. All cameras got soaked, yet performed without a problem. I occasionally wiped them off with a handkerchief and draped it over them, when waiting for the action to start.
Also present were press shooters armed with the usual selection of weathersealed pro bodies from Canon/Nikon. As I mentioned, it was pouring down rain, but none of them gave it a second thought.
This got me thinking.
Even if my M6 had gotten completely soaked it would have continued to shoot and after a night of drying would have once again been fully operational.
If on the other hand I had been shooting with a pair of M9 bodies, what would I have done?
The M9 isn't weather-sealed and crammed with electronics. If the M9 gets soaked it will either shut down or short circuit.
Shutting down is a temporary problem, but once the water evaporates it leaves behind minerals that could promote corrosion. You may also lose some very important pictures, because your camera ceased to function at a critical moment in time. If the camera fries itself you are facing a very big repair bill (if you are no longer covered via Passport warranty) and the loss of the camera for several weeks to Solms.
I've said this before and everyone is probably tired of hearing me say this, but I find it mind boggling that in this day and age Leica would produce a digital M body that isn't properly sealed. The M9 is billed as a professional camera. It costs $7500. It is not weathersealed, so essentially you are playing Russian roulette, every time you shoot with it in inclement weather. How retarded is this? Even Pentax manages to weatherproof their sub $1000 models. And no, adding sealing would not change the appearance of the M9, nor drive up the cost by another $1000 or more.