That 5V feeding can be done to 5V (after regulator).
A such power supply must be exact same voltage as regulator pots out.. I'd not recommend such a solution.
Alternativ may be to cut the trace bringing 5V to 'the line of 5V', and then feed this line from your external source.
..or is this your shield.. http://www.robotshop.us/media/files/PDF/dfrobot-arduino-shields-manual.pdf