I understand what you're saying. I'm OK with getting 80% of the skills now and the ocean-specific 20% later.
What I can do is practice some of the skills with my husband (already Rescue certified in a lake) on an ocean boat dive later. The rescue breaths and tows we could practice on any surface interval, as long as we clear it with the captain and DM so they don't worry. I wouldn't try the panicked diver or getting an unresponsive diver onto a boat without some very experienced divers supervising/helping, though. Sometimes we dive with friends in North Carolina who are DMs/instructors/technical, and they might not mind a little extra adventure on a surface interval one of these days.
Navigating search patterns, finding a missing diver, and surfacing a diver are actually more difficult in a lake with poor visibility, so that part will be good to do in a lake.
I had a look at my log:
Fresh water dives (mostly < 20ft visibility): 19
Ocean dives: 14
Aquarium dives (not a pool): 2
Warm water (over 75 degrees): 17
Cool water (60-75 degrees, all in fresh water): 16
Cold water (below 60 degrees, all in fresh water): 2, and I didn't like it
What gets me is not just the cold water itself. It's the 7+7mm wetsuit and the heavy weights that go with it. Hauling around that extra weight is hard on my knees and ankles (32lbs of lead in fresh water last time). It's also beyond my BCD's lift capacity. You have to pay twice as much attention to buoyancy control too. If my buddy's life depended on it, I might be able to pull off a rescue in that environment, but I might also hurt myself in the process. It's just too much, sorry. You CA coast divers are tougher than me. We're only here temporarily, moving back to North Carolina this winter.
It's a good idea to take Rescue in warm ocean water, but I don't think the cards would line up for that for another year or two. It's hard enough to leave the kids with my husband for two days locally!