Is there anyway to make your endorser only inject endorsements for priority 0 blocks, and not inject for priority 1 or higher ?
There isn't an option to set a max priority like the baker binary does. This is because there shouldn't be a good valid reason to do this. The endorser by design will endorse the highest priority block available since doing so yields the greatest reward. By choosing to not endorse lower priority blocks, you'll miss out a lot more rewards that you could had otherwise earned.
If the goal is to avoid the rare case where your endorser prematurely endorses a lower priority block that yields a losing chain, that fear is not merited. By design, these occurrences should never happen as there is specific time windows where each priority can bake based on the previous block. The time windows for different priority bakes shouldn't overlap, at least your endorser won't acknowledge them as validate. As long as your node has all the propagated operations known to the network, the endorser should not endorse the "losing" chain.