Eddy - I don't think that it's very novel, but to go from 0-5V to -10-10V I would use an op amp in a similar way to the link that Jonathan gave. Personally, I would do it slightly differently; the op amp needs +-12V to make sure that there is enough headroom on the output (unless you find an op amp that can work closer to the supply rails). Use a potential divider across the supply rails (or +12 and 0V), with whatever regulation/zener diode etc you like, to give a fixed 2.5V and connect this to the inverting input via R1. Use a feedback resistor R2 from output to inverting input. R2/R1 = 4 to give correct gain. Take the 0-5V via an appropriate resistor to the non-inverting input. Job done - I think. You could incorporate a bit more smoothing if you are using a PWM analogue "pseudo 0-5V" signal by putting a suitable capacitor in parallel with the feedback resistor.

You would then use this on a 0-5V output from a BOB connected to the LinuxCNC system and LCNC would allow either gcode-controlled speed or could be overridden for manual control from the LCNC control panel. I think - I use LinuxCNC but don't have speed control that way yet (just use VFD controls manually) so I'm not familiar with that bit.