My sister has one of these Thermomixes, and I've had a bit of a look at it.
I reckon you could fit about 0.5 - 1.0 kg of grain in the inner basket, with about 3 lt of water in the main chamber, enough so all the grain is covered in water.
Pre-heat the water to your mini-mash temp, then put the basket full of crushed grain into the Thermomix, and get it to sit at 65 for an hour, with the rotor on lowest speed.
Then pull the basket and the grains out, and ramp the temperature up to boiling for at least 10 - 15 mins to sanitise.
Tip the boiled liquor on top of your Coopers kit.
Give it a try, and let us know how you get along. Could be an awesome technique for people wanting to try out really, really small batches.