I have been thinking about this.

I am planning to implement something like:

When you park in an underground garage you won't have a good GPS fix.
The 'waiting for an accurate position' page will get a button <I am in an underground garage>
When the button is pushed, A dialog opens where you can enter the name of the garage, the level, the row and the lot-number.
The name of the garage is stored on the server, along with the inacuurate network-position that will be availabe.
The next time someone parks in the same garage, the name can be chosen from a drop-down list.

Alternative ways to get the location of the underground garage are:
Use the last known accurate location prior to entering the garage
and/or
Use the first accurate location after leaving the garage.
and/or
Find a database containing locations of underground garages and integrate that with EasyPark

Jaap