Yeah, no snap-on to convert them to clip-n-strap. At least none made by speedplay. There are some after market companies that make something for triathletes that holds the entire shoe so they can attach their running shoes and not deal with changing shoes in the second transition. They may make something for speedplays. They look stupid though. (Stupid as in only a triathlete would consider using them)

Like pitboss, I've seen several methods for securing just straps to them. Some require drilling holes. Wouldn't recommend it unless (a) someone else will buy you a new pair if you screw them up or (b) you generally have a problem with your leg strength overpowering the retention mechanism.