It turned out to be very straight forward. Here are the steps.
Create a working directory, place an update file in it (built with TFR METAR only checked), unblock the zip file then unzip the zip file (which will create a sub directory).
Go into the newly created sub directory and double click on the TFR.xml file to open it in Windows Explorer. Search for a TFR you want to use. I use the Disney World one as I know where it is and know to always avoid it. Once you have searched to the Disney TFR search on which will take you to the description of the TFR area as used to actually draw the displayed area. This follows the Disney title to the TFR you searched on by a good bit as there is a lengthily description of the TFR.
Edit what is between the BOUND statement. I used the following to outline the first aerobatic box.
<BOUND>RLN26.809444W80.378611LN26.750000W80.378611LN26.750556W80.282778LN26.781389W80.321667LN26.809444W80.378611
I just read over the spec linked from above and it answers all questions about what shapes can be built and just how to build them. Thank You!!
BOUND>
I also edited the name of the TFR to say my aerobatic box and changed the altitude min and max just to see if it would all translate. I then saved the updated TFR.XML file.
Move back up one directory level, rename the original update zip file to something like .zi_ to create a backup and then zip the subdirectory to create another update zip file which includes your modifications.
Perform a normal USB stick TFR/METAR update to your GPS using this newly created file. The newly defined TFR should appear complete with your naming and altitude min/max values. I plan on setting the airspace notification function in the latest version of software and testing the GPS' ability to keep track of when I am in the box.
It is worth noting that this process does not edit the SD card but only modifies the standard USB stick update process file. It is easily backed out by simply doing a normal TFR/METAR update and installing it as usual. This will overwrite your custom TFR area. My next step is to play with the color settings (I already have the box being displayed as a red shaded area which shows up very well in Vector mode) along with changing two of the sides to arcs as these sides are actually the arc boundaries of Class E airspace.
I'll try to shoot a picture of the results.