It won't be that exciting - just 4 holes drilled in the case!
Seriously, in terms of mods this is about as easy as it gets. You don't even have to modify any circuits and the soldering is minimal. The trickiest part will be drilling the case nicely.
All you have to do is solder a header to the holes in the (many) pictures above and run a ribbon cable from that to the jacks, wherever you decide to place them. Personally, I will probably use 4x 3.5mm TRS jacks between the USB and power jacks. There's not enough room (as far as I can manage) for 1/4" jacks – there is a large header that would block the jack body and there's not enough vertical height to mount the jacks above the header.