A method of random selection ?

Draw names out of a hat.

You could do a variation on normal methods, like Alphabetical order, but starting from the fourth letter of students names, or their street names.

Draw a map of students sitting position in class and then draw a face on the map, choose students who sit closest to the face lines; as long as the person who draws the face does not know where people sit it would be a random result.

Ask students to work out the day of the week they were born on, then choose by T days, weekends, Wednesdays, or if they know morning or afternoon births.

As long as the result is not reasonably predictable, its random.

One problem is the cut off point to get just 30, so you have to have a secondary criteria, like closest to the half hour in the case of afternoon births. People need to commit to their identifying data before the criteria is announced.

Any computer program besides excel

A random number table

An algorithm involving dice rolls

Names from a hat