My solution to this problem is relatively simple, my kid moved teams. His HS Varsity coach is also his club coach, problem solved ... just play wherever the coach tells him.
For the record, there are really 3 types of game like events.
1. "inter-squad scrimmage" aka practice - scrimmage game between varsity and jv or jv and freshman, these don't count and you can have an unpaid guy in a referee's shirt managing the scrimmage.
2. "interscholastic scrimmage" - training session between two to three schools. Includes, a single Alumni game. Can have an unpaid official. Must be played before team's first interscholastic contest. Unpaid referee only. Does not count against the 20 contest rule.
3. "interscholastic contest" - non-league, tournament or league game. Maximum of 20 contests, not including playoffs.
With regard to Club overlap (BlueBook SS):
Rule 2509 - During Individual’s Season of Sport - A member of a high school soccer team may not, during his or her season of sport, compete for an outside team in the sport of soccer. A season of sport (see Bylaw 504) is defined as that period which begins with a student’s first interscholastic competition (nonleague, tournament, or league game) and ends with that student’s last interscholastic contest (tournament, non-league or CIF Southern Section playoff).
For our purposes in 2018 that is November 12 for the Southern Section (including SD). In other words, a Club/HS player can practice through November 11 with both teams and play a club event through November 11. If the player continues to play club they cannot "compete" for the HS.