Really, you don't need to bleed it at all, if you are careful.
1. Drain the reservoir with a syringe or turkey baster or siphon, or whatever...... mop out the remaining brake fluid with paper towel so that it's dry and there's nothing left to spill.
From this point DO NOT TOUCH THE MASTER CYLINDER LEVER of the unit you are working on until step 5.
2. Detach the OEM reservoir. Be careful of the fluid left in the reservoir-to-master-cyl line.
3. Mount the Rizoma reservoir and attach the line.
4. Refill the Rizoma reservoir and flick the line with your finger, or tap it with a screw driver handle. Some bubbles may be seen escaping into the reservoir.
5. Gently pump the lever.... first move it only about 10% of pull a few times...
............then 25% a few times...
............then pull it hard a few times.
You will see bubbles come into the reservoir sometime during this operation.
If you don't move the lever before you refill the reservoirs, the master cylinder will not see air, and all you need to do is purge the little bit of air in the reservoir-to-master-cyl line.
Worked for me............. and replacing the 999's integral reservoirs with the remote units is a bit more tricky because that line is new and totally dry. Still no need to bleed.
I did have the benefit of clear brake-fluid line so that I could see the fluid displacing the air.