I wasn't trying to avoid your question but to provide alternatives to what seemed to me like a bad idea. Why would you require boots with clips but only running shoes with clipless pedals? Why are you willing to waste money chalking something up to experience but then not willing to spend money on getting the right thing?

As far as something to put in your shoe, kevlar seems like it would be the ideal option. Anything less seems like it would either just get torn through or be too thick. You might also just stick a plate or some extra large washers inside, since comfort doesn't seem to be a factor.