...2 SPs in Tacoma on a moment's notice signals to me (minimally-educated guess) that JeDi is more flexible than this. Gallardo is his preferred use of Sunk Cost, but he's not married to 10-12 starts, no how. And it's not necessarily the ERA he's looking at (obviously - not putting words in anyone's mouth here).
I think JeDi has a mission for Gallardo. He sees a problem with the man's game, and has a minimally acceptable class of result he expects from Yovani. Return to form is a bonus, not an expectation - we're looking for a guy here who can keep our offense in the game without shutting the other team down completely, yet in an manner which still gives the bullpen odds for an easier night.
That said, the manner in which Yovani reaches his steady 4.x ERA is what's going to determine the call here. If cool weather and a fresh lcoation are still making every game a nail-biter, and if the fixes dreamed up by Servais and co don't function OR aren't being followed... that's what gets the #5 SP carousel started sooner than later IMO. And I'm guessing Jerry sees enough potential to take the shot (upside for sure!), but enough of a down-scenario to be prepared from Day One.