Speedplay zero toe strap adapter?!?
 

Is there such a thing? I see on performance bike they have the Dimension Instep Pedal Insert - Shimano SPD (also for LOOKs). Nothing for Speedplays.

This bike is used mainly for winter training and I keep Speedplays on it permanently. Occasionally I would like to hop on in normal shoes without having to switch out the pedals. Is there anything out there?

If you are freewheeling you can do this. Otherwise, take that idea and craft your own toeclip set up with old cleats and some toe clips. Or just buy some touring or cheap MTB shoes and install your cleats (assuming Frogs here).

I have Speedplay Zero's and when I bought them I also picked up a pair of converters that make them a platform. They are a plastic pedal with a large C clip to secure to the pedal. Ask in your LBS if they have them. Work fine for me.

the only strap-mod I have seen with the Speedplays it where a strap is secured using one of the pedal screws - and this was done for track racing for pedal foot retention while sprinting

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.