It depends on when you want to him to meet you. For example, if you get up to WA by the start or middle of August (and I’d encourage you to do so), then the route from Snoqualmie Pass to Stevens pass is super scenic and can be done easily by a non-thruhiker in a week.
But, maybe you don’t want to try to time things that way. Personally, I think the desert is super cool. So, I’d have him meet me in Agua Dulce and hike to Mojave. I really liked the aquaduct and think it is a pretty unique environment, at least for people not from around there.
NorCal is nice, but harder to get to, especially with a shuttle. However, the link from Dunsmuir to Etna is nice and you can probably get something going there.
Personally, I’d want to meet him as early on as possible so I don’t have a “Must be here at a certain time” hanging over me. So, why not from the border to Warner Springs or Idyllwild?
Suge