What techniques can be used for laying plates at 45° angle? I've seen a number of techniques for laying individual elements at 45° angles, but I need a consistent method for laying down larger plates at 45 degrees while maintaining close contact with the base plate layer below it.

What techniques are available to achieve this?
Hinges can work, I have used this technique before, if you sandwich the hinges between two plates you get 45 degree 'bricks' that are quite solid.  

In most cases, tiles and plates in the right place will keep sufficient contact with the base plate to have a stable model.