To be honest I wouldn't worry so much about overtraining at this point. Most people don't train nearly hard enough to reach a truly overtrained state. Doing some pre-exhaust sets for your chest is very unlikely to overtrain you. So, yes, you can do it every chest workout.
What people mean when they say that pre-exhaustion should be used every now and then (or at least how they should mean) is that it's a tool to help you activate/utilize muscle groups which you are otherwise unable to activate/utilize. So, if say your lats and chest weren't seeming to get pumped during your workouts (or you couldn't feel them working) or weren't growing in proportion to the rest of you then you might incorporate pre-exhausting them to help with this. Your other muscles that you did feel working/were growing in proportion though wouldn't need to be pre-exhausted and doing so would only cut into your recovery abilities/add more unnecessary fatigue throughout the week. Make sense?
Good exercises to pre-exhaust with would include any isolation exercise for the chest (DB flyes, cable cross-overs, machine flyes, peck deck). I personally prefer cables or machines because they allow for constant tension and for you to really squeeze the chest at the fully contracted position; flyes (like all free weight exercises) are dependent on leverage and gravity and thus do not allow for as large of a range of motion. But, it's a matter of preference.
If your upper chest is lacking the most, you might want to try cable cross-overs starting from low to high, then once having done a few sets (and having pumped a bunch of blood into the muscle and increased your ability to feel it working) move onto your incline pressing (you could do both BB inclines and HS inclines back to back, or still do the HS incline after flats, it's up to you). By the time you move on to flat pressing your chest should be sufficiently pumped (and you should be able to feel it working). If not you could always throw in a set of high to low cable cross-overs (or whatever other flat fly movement you wanted) prior to doing your flat pressing.
Here are the low to high cable cross-overs:
And here are high to low cable cross-overs: