you don't want a shotgun...
is that because you want an omni pick up?
is that because you don't want to ruin the small form factor of the m?
is that because of cost?
I have two solutions:
use the m's built in mics, but stick a couple of these over the pick ups:http://www.rycote.com/products/windshield-solutions/micro-windjammer/micro-windjammer/
cheap, compact, omni.
or (be warned, this is a shotgun mic)
a sennheiser mke400d. Calumet had them and were selling them off quite cheap.
For a hypercardiod it is very compact and frequently copied. runs on aaa, and sounds fantastic, there is also a rycote for it as well.
It has been superceded by the mke600d which is much more like a 416 or me66 in terms of shape and size, ridiculous on the m. Quite costly too.
Unless it has Shure, AKG, Rode or Sennheiser written on it, it probably isn't worth buying at this end of the market.
I have an old sennheiser mke300 that I break out for the very rare occassions I use a camera top mic (usualllty i'm a lav or stand guy) and despite being 20 years old, still does the business, very light, very directional, and insultingly cheap used on auction sites. Plastic built so very light, but very very high quality mono hyper pic up.
I would have one of these ahead of a new mic costing the same.
Sound is one area where economy reveals itself, if its important enough for you to have asked the question then its important enough to buy the right thing...
2 scenarios, 2 solutions, both of which i can personally vouch for.