Suppose you took a SPD pedal that has a cage like a quill pedal - Shimano M324 for example - and attached toe clips with loose straps to the SPD side - in other words, to clip in you insert your shoe into the clip then step down.
Would this work?
Why bother? Two thoughts. First, maybe you want the choice of riding in either clipless cleats or in non-cycling shoes plus the added security of toe clips. Second, maybe you have a vintage bike that just looks wrong with clipless pedals.
I think I agree with Fiets (it's hard to tell). When using the SPD side of the pedal, the toe clip is likely to hang down and scrape the ground in turns. Annoying at best.
If you want to try it, my wife's bike has M324 pedals. She's not using it right now (long story) so I'll loan them to you for testing purposes.