If anyone is interested, my friend and I developed a Cura post processing script (he did the hard part). I really think this would be better off a firmware feature, like I wrote a request for. But, in the meanwhile, for those using Cura:
You pass it a single parameter (mesh spacing value), and it parses the first layer gcode for min/max X and Y coordinates, and then replaces the M557 line in your start gcode.
Just remove the .txt, and drop it here: C:\Program Files\Ultimaker Cura 4.5.0\plugins\PostProcessingPlugin\scripts\
You must have a static mesh leveling command in your start gcode, like: M557 X0:200 Y0:200 S20