My booty call shows up randomly?

So I have a freind that we use to work together. It was kind of a place that use to house us, so we all kind of lived on the same faculity. They came back after some time and niether of us living there anymore and well we got drunk and slept together. They now show up randomly every so often and it kind of just happens. I am not horribly upset with this arrangement and I work and am at school constantly. So I know a real relationship is probobly not doable. However, is there a way to get them to show up more consistently? Since sometimes they show up and I like have work the next morning.