If you want to get close to the same look and info as you get from the built in tooltip pop ups on your custom maps, here is how to come close. The code is in the attached txt file. For more variables see this post The specified item was not found..
The reason I ended up doing it this way is because it seems there is a 1681 character limit for all three boxes total. I couldn't get the right look/format using html table commands. If you only want to use one box or want to cut back on the code, you might be able to squeeze it all in and not have to worry about the external css style sheet. I couldn't figure out how to call my own custom style sheet, so I just added to an existing one. The plus is you can put a lot more code in the edit map tooltip boxes. The negative is that the css style sheet gets over written during service packs and upgrades. You just have to remember to paste the code back in. So if you add or alter my provided code, remember to keep a copy somewhere.
I also couldn't figure out how to get icons and bars as in the standard popup tool tips. Someone might be able to add that info. The code has to be out there somewhere and get called, I just don't know enough to go find it :). It took me many many hours just to get to this point.
See screen shots below and enjoy.