I'm a little skeptical of this whole enterprise.
If someone likes foot retention and wants to wear regular shoes, toe clips and straps are the solution. But there are no clips-on-one-side-clipless-on-the-other pedals.
But if someone is used to riding "free" on platform pedals and doesn't seem interested in foot retention of the clipped or clipless variety, I'm not sure that buying them clipless pedals will lead to them being used.