I've never worked on a Super, but all other 105 series spiders and sprints that I have played with use allen screws to hold the two halves of the steering column shround together. Metric allen screws, naturally.
As I recall, these screws are in at least two different lengths (the pair on the left side is different from the pair on the right side), and they are fairly unique - that is, if you lose one, you won't find its replacement at the corner hardware store.
You will need a metric allen wrench with some length on it to reach up into the holes. I want to say it is a 3mm, but not sure right now. Remember which bolt goes where as they are different lengths. Don't over tighten when you put it back together as the nuts are just held in thin plastic, as they are easy to strip out.