You could pull vacuum over the oil bath to positively coax all the air bubbles out of the watch.
Unfortunately, that would also destroy the LCD and quite possibly the crystal oscillator (not sure how strong the metal can enclosure of those things are). Battery wouldn't survive it either but you could easily take it out and insert it after the vacuuming.
Filling this with mineral oil might actually reduce rather than increase its pressure withstanding ability.
Hopefully someone does some tests.