I was planning on doing this myself for two players who aren't in my current Runelords game. However, do note that Mythic does not singlehandedly make up for a lack of bodies. You might wish to also provide them with a higher point build (25 points instead of 15). Also, it depends on the classes they choose (I personally hate gestalts as I find them to be cheesy and unbalanced); you could include a non-Mythic GMPC to either fill any void left by the players' class choices (Bard is usually a good choice). You could also start the players off at 2nd level and instead of using XPs have them level up when the AP recommends it but keeping them at +1 level.
Then again, I'm also planning on having the players Ascend upon finding the Runewell as I consider it a natural point of Ascension. You'll likely want to fudge rolls on occasion until the moment of Ascension as two PCs can easily be overwhelmed if you're not careful, even with higher stats and a higher level.