Ordered three cheap volt/amp meters from ebay and hooked them up on my Hephestos, top one is for Arduino, motors and extruder, middle one for heatbed and bottom one for my Raspberry running OctoPrint.
Take out the top to screws of the Z-axis and replace with longer ones. Then place the holder for the meters and place two bolts.
Wite up the whole thing and make your Hephestos bling even more :)
Youtube video: https://www.youtube.com/watch?v=LNqEQS4OY8M
Update: added photo of meter connectors and Fritzing drawings
May 6 2016: added the 123D design to the project