Anyone know anything about disc brakes?

• unbolt the lever from the untapped bars
  
• unbolt the caliper from the frame
  
• bike in stand, horizontal unbolt hose from caliper. As soon as hose is released point it upwards so it can't drip.
  
• remove caliper (you can cap it off with the right sized screw if you want)
  
• position bike vertically with hose facing up
  
• draw hose through the frame and out
  
  

It's all about using gravity to keep the fluid where it needs to be. There's surprisingly little of it in the hose. I suspect there is a bolt out there that would cap it off, too. Have a poke around.

You will need to do a proper bleed on reassembly though - very unlikely you won't get air in the caliper and hose during the process.