Here's what happened when I tried it: http://chipmusic.org/forums/topic/15989/lsdj-on-3ds/

I was using Shantae, another game might be better suited but AFAIK this has been patched.

Gonna give this a necro bump.  With some of the leaps the 3DS community has made, does this seem more feasible?  I know it's possible to inject GBC ROMs into the VC games and it's possible to make unsigned GBA VC titles.  Could an installable CIA of LSDJ be created?

I've had some success using LSDJ with Lameboy emulator on 3DS, but you will need a proper flashcart - I.e a DSTwo, or other 3DS compatible card.

You wont be able to do it without a flashcart, sorry. I wouldn't even bother with LSDJ as it doesn't sound too hot when emulated. There are some more interesting/better music making apps for the 3DS already. You can get them through the iStore thing. Check out Rhythm Core Alpha 2 and the 2 current Korg products.

I have a "normal" CF card, but no flashcart for the 3DS.

I was hoping to load it from my Mac with an USB cable or via WIFI (connecting devices etc)

if you have an early enough backup and a flashcart, yes.

Hi!

   Is there a way to load LSDJ in a nin 3ds?

I've looked and the latest I could find was a loader for an emulator along the LSDJ for a DS, dated sometime in 2013, and the guy saying that most likely someone would patch it out for the 3ds soon.

  I really don't want to buy something else if with what I have can use it and at the moment it's impossible for me to get a hold of a GB or a cartridge.