There's a video of Nullsleep playing Her Lazer Light Eyes with an LSDJ keyboard like you describe. It's pretty cool.

The video of Kineticturtle shredding the keytar, however, is far more impressive!

You could make your own LSDJ keytar by putting a guitar-strap on an LDSJ keyboard.

When I say LSDJ keyboard I mean one of these -

I've made my own LSDJ keytar like the one I'm trying to describe but sadly I don't have any pictures.

Mine was really ghetto.

The guitar-strap was made out of black duct-tape and the keyboard had a GBC duct-taped to it.

I would take some pictures of it to show you but I had to leave it in my storage unit in Cali when I moved to Miami.

If the keytar has MIDI out, you can use it with ArduinoBoy + mGB. You could use LSDj as well, but it isn't really the preferred way of doing it in my opinion. (Instead use two cartridges and two 'boys.)

I do this in The Glowing Stars.
Arduinoboy mini with MGB into a Roland AX-1. I usually have the AX-1 set to output on two MIDI channels at once, and set the two PU channels an octave apart with different duty cycles, and it sounds pretty fat.

MGBs assignability of parameters for live use is pretty limited though, so you'll want to do vibrato by tapping the pitch ribbon. It's pretty expressive once you get used to it. The mod lever will only control duty cycle, and it's almost impossible to get anything other than full on or full off.

yeah sorry, wasnt really sure where to put it, thanks though.

oh, forgot to add that with arduinoboy & MGB, you could have midi control over your game boy also

do not post twice, and neither is really in the right section. moved for you
now for your question: using a MIDI->GB or LSDJMC2 (or arduinoboy, i believe) in keyboard mode with the out from the keytar should give some amount of control over LSDJ (read up about keyboard mode in the LSDJ manual)

Does anybody know if its possible to control lsdj or gameboy through, say a Roland AX-synth?