Having participated as a mentor in another organization, and having seen the application process every year, I can say that the main part is coming up with a webpage full of ideas for projects. I think that already exists partially on the ocamllabs wiki. I'd really like to see that wiki be centralized and available from the
ocaml.org site. The key thing is to figure out which projects are doable by people in one summer. The next step is that people need to volunteer for mentorship. Even 2 people are enough for a start, but 3-4 are better. Finally, one person takes on the process of filling out the application and submitting it.
One of the things that concern google, as can be seen in the webpage, is that there's enough effort from the mentors to
a. weed out the poor candidates and
b. be in touch with/demand enough from the candidates to make sure that they're actually working and not just slacking off for the summer. In my old organization, the participants had to post blog updates every week or so about their progress.
Other than that, there's not much to it.