I remixed funkymonk's 3DR Simple spool holder to incorporate holes on the underside of the main hub along with corresponding nut traps. These are intended to enable central mounting of a controller board underneath the spool holder as the RichRap's original 3DR allows.
I am prototyping a Ramps 1.4 mounting bracket for this as I type. I will create that thing and link to it here as well.
The mounting holes can be used for anything, really.
Print it and install M3 plain nuts into the traps.