Probably not as a full member, but a "half member" or "associate member" of the conference or a contractual scheduling agreement - whatever language you want to use

Imagine the PAC extends an invitation for the following to Hawaii

• Scheduling Agreement where 8 PAC teams will play @Hawaii every year
• Hawaii will receive 1/3rd the media rights (so say $8M on a $24M/yr/school deal)
• PAC will have rights to all (home) Hawaii games (both those 8 with PAC teams and any others Hawaii happens to play)

From the Hawaii perspective, it's a huge win

• They go from making $4M/yr (MWC) to making $8M/yr. 
• They have (minimum) 8 home games against P5 opponents - nice for tickets/concessions and reduced travel costs
• Increased quality of competition
• Other 4 games per year can fairly easily be filled, especially since they don't NEED more home games
  • 1 for 1 with MWC teams
  • 1 for 2 with other P5 teams
  • 0 for 1 with high-end P5 teams for a paycheck 

From the PAC perspective, it's likely also a win, mostly by taking advantage of the Hawaii rule

• They're paying $8M to add (a minimum of) 8 extra games of inventory (plus they'd own whatever extra home games Hawaii schedules), so would likely make that up (and much more) in any negotiation
• The time slot isn't ideal, but it's one that could potentially be useful anyway (per this article at least)
• Extra practice time - teams can't officially start practice until 4 weeks before their first game - with 8 PAC teams now having a Week 0 game, that means an extra week of practice
• With 8 PAC teams playing in Week 0, the PAC could dominate the viewership in that week with unopposed football and shine a spotlight on the conference to open the season.  For one week every college football fan would basically be watching a PAC game and every station would have almost nothing besides PAC games to show
• Recruiting benefits
  • In a 12 team PAC, this would mean players would get a trip to Hawaii 2 of every 3 years...  People like going to Hawaii. Not a huge thing, but a nice little perk
  • This would mean that pretty much ONLY PAC teams would be playing in Hawaii (with rare other exceptions) which could help push PAC toward the forefront of Hawaii/Polynesian recruiting

Also, as a small note, Hawaii is an R1 Research University with R&D Expenditures on par with Oregon St, so wouldn't be a non-starter academically.  Hawaii could also benefit by having an affiliation with stronger academic mainland schools.  Academics doesn't drive anything, so consider this more of a footnote, just pointing out that it doesn't scuttle the deal