Ain Maavirim Against Makom Kavua

What is the halacha for a person who has to go to shul A at 6:30am for selichos [which will be followed by shachris] and then wants to daven shachris in shul B which is where he normally davens, at 7:00am? May he leave the first shul, thus transgressing אין מעבירין על המצוות  - passing over the mitzva that is in front of him in order to fulfill the inyan of davening in his makom kavua? Or do we say that he should remain in the first place since he is already there and אין מעבירין על המצוות?

It would appear that he should go to his regular shul for shachris based on the Chazon Ish [Menachos 15/3] that when there is a conflict between תדיר [what is more common] and אין מעבירין - we follow the תדיר. In the same vein, we tell him to attend his regular shul which is like תדיר.

[Rav Genechovsky ztz"l]