When I had my Duetto I just used a mirror from my girlfriends make up stuff (powder thingy) and thought about it, I'd have to just run a mirror at an angle with a lot of it resting on the rim of the cup. It's not as easy, but it can be done.

The MCAL similarly makes it hard to mount a mirror on the machine behind the group. My solution was to place a small mirror in front of the machine on the counter, which works very well. Depending on your counter height, you might need to prop it up at an angle to make it ergonomic.