You do know that in order to get that second permit, not only are you going to have to pick it up after 11am the day before, or prior to 10am the day of, you need to go all the way to the Valley or south entrance to do so? Also, technically, if the permit is in your name, you're the "trip leader", and you're the one that has to sign the permit.
You should just piggyback your 6 days off the Ostrander permit or make that your replacement entry trailhead for Red Peak as well. Swapping out your reservation for what you already have with a new walk-up permit isn't likely going to be a problem up there ( Ostrander Lake reservations for August are virtually wide open
https://www.nps.gov/yose/planyourvisit/ ... lheads.pdf ) and a diversion for a night up at Ostrander isn't going to affect your Red Peak trip in any measurable way. They care a lot about where and when you enter, but where and when you exit is primarily up to you. Adding days is no big deal.
If you really want to max out the elevation benefit of being at Ostrander already, you should hit the Buena Vista up higher and continue cross country over to Lower Merced Pass Lake, then pick up the trail over to Ottoway and Red Peak from there. It's not that much further than what you were basically planning originally in hitting the Illilouette, so why drop in elevation more than you have to when some creative route finding will get you to where you need to end up anyhow? All you really need to do is plot a course slightly E/NE in a straight line between the two points and follow your heading as terrain allows.