I have a device (the Griffin Powermate) which is a very flexible little
gizmo.

It probes as a HID, and all I can do with it is left-click, and move my mouse
very slowly left and right.

What's the correct strategy?

1.  Tell wscons not to use this device.
2.  Tell uhid not to probe this device.

The former sounds hard; I'm not sure wscons is given access to the device
ID strings or anything like that, so I'm not sure how I'd tell it "don't
use any mouse that says it's a Griffin Powermate".  It also sounds cleaner;
the alternative is to either write a new driver, or do something magic with
the ugen driver.

It seems to me that, if this device were probed as a uhid, and *not* turned
into a mouse, that I could use it.  It currently shows up as:

uhidev0 at uhub0 port 2 configuration 1 interface 0
uhidev0: Griffin Technology, Inc. Griffin PowerMate, rev 1.00/1.09, addr 3, iclass 3/1
ums0 at uhidev0: 3 buttons
wsmouse1 at ums0 mux 0

-s