Can I clear Fort Hood while I am on PCS leave?

I have heard of it, but I would highly not recommend it, as leave is what happens at the end of the process and to be on leave during it, is burning your leave. So I would clear and go on leave once finished is my advice.
Part of clearing is being at the house to help your wife out and ready your affairs or tend to whatever you think you would be doing if on leave. Clearing is not only sitting in line at some station waiting to get records or a different block checked. Save the leave and use it once in Europe.
If you have something going on, some locations will allow you to clear very rapidly and go on leave once finished. The bulk of clearing can be physically done in a day or two, but often what holds people up is the movement of hhg's or they hit a snag at cif or finance. All across the Army people are given 14 days to clear and everyone knows the vast majority of that time is spent at the house readying the family and not just getting block checks.