Ed,
At MKE you're stuck with $ignature - And you know how I feel about them.
There are several other options that are much better. MWC and UES are both close to freeways and will allow you to drive to MKE the easy way, but the closest airport is actually RAC. All three have cars. When I need to do something in Milwaukee I just pick whichever of the three is closest.
If this is for an Angel/Lifeline flight, you could try calling ahead to see what they'll do to you, but I doubt that they'll waive anything. Barring that, find out which hospital they're at so you can see which airport is closest - Columbia/St Mary's or St Joseph's use MWC, Froedtert use UES, St Francis use RAC, etc.