Yes, that site is Peter's. At the top of this page,
Aviation, there is a link to another site with various information and discussions on cloud tops etc... I only have an IMCr and don't do much in the way of high altitude IFR 'touring' myself, but the GRAMET site specifically seems the easiest to use. The images display to a point if it overcast or broken, but I don't think anything really is going to be 100%.
I think it's a case of just making sure you are between layers, particularly if you don't have FIKI, or having the capability to out climb any weather or know where frontal weather may occur.