This is for people who have slow machines, there are much better/faster ways of doing this in Maya but you need a nice fast machine in order to go about it. Anyway…
Select your model and Go to Window/ UV Texture Editor
Go to Polygons/UV Snapshot (Hopefully you’ve already played around with your UVs) Save your snapshot somewhere.
Using Photoshop or what ever Photo editing software you have, edit that Snapshot. Paint the parts that you want bald black and the rest white (or grey if you want it to be kind of bald, you know what i mean)
Go back to Maya.
Open your hypershade and load the snapshot onto a blinn or whatever. Right click on your blinn and go to graph network so you can see a picture/node of your snapshot.
Go to Fur/Edit Fur Description and click on your fur description name. Go down to where it says Bald. Now drag the pic of your snapshot from the hypershad onto the bald section. Once that’s done go up to Bake Attribute and select ‘Baldness’ from the dropdown menu. Then click on Bake.