Admittedly, I'm not familiar with these newer 'tank' based systems, but assuming this is a inkjet, the rest should be the same.
Have you run any prints and has this gone thru a cleaning cycle? If not I would like to think just remove the tanks and youshouldbe ok.
If it has, can you purchase empty 'tanks' to fill with a cleaning solution (IPA, ProGly & distilled water) to flush the system out?
You should be able to disassemble the printer enough to get to the printhead and remove the feeder cartridge block (the bit that looks like a moulded pack of cartridges) then use a tapered needle or adapter that'll fit the outlet nozzles on each cartridge block outlet, with a syringe to suck all the ink through and purge the system.
Once you've done that I'd recommend sticking about 10-15ml of your dye sub inks into each of the reservoirs (correct colour for each, of course!), swill the ink (and printer) around to mix any remaining ink together and then pull that through using the same technique as before. Dump all the ink pulled through, reassemble and then fill the reservoirs with your dye-sub inks and prime everything up before printing off a bunch of rough draft stuff on scrap paper to clear the system through.
It's a bit of work but failing that you could look at disconnecting the reservoirs and just using external bottles as the reservoirs instead. You'd still need to flush the cartridge block through as much as possible though.
Hope that gives you some options to consider...
There's tons of videos on the earlier 2720 model btw... so just check youtube for inspiration.