|"Can you / should you practice more than 1 religion at a time?"|
But just as soon as I developed this thought, I was almost seemingly divinely answered by the Dalai Lama himself.
The part that refutes the notion of practicing more than one religion is the necessity to become immersed and develop a "deep feeling, making them part of one's inner experience." Can you truly incorporate and draw from the depths of multiple religious views? Not even God himself (or Allah or Buddha, etc.) had that ability. So maybe it's best not to even try.