So I want Deacon's approval for his perk, and I'm playing against type to get it (I'm ordinarily a brutal drug-taking cannibal who wants to side with the Institute, I suppose you could justify my character's interactions as going undercover to get close to a Railroad insider).

However, it seems to be taking a while. Any indication of how many "loved" interactions from the wikia page need to be completed or how long it takes to normally unlock one of these perks? Any tips to make the process faster (I'm already steering clear of all the hated/disliked interactions)?

Depends from your actions, required affinity is 1000 to obtain the perk but no idea how every action does affect it.

Basicly he should be talking with you 2 or 3 times with an unique dialogue line, before you obtain his perk.

Doing some RR missions with him along, even radiant ones might help raising it fairly fast, remember i maxed so many companions just standing at the weapon's workbench , no clue if it works with him tho.

Just got the first one of his special dialogues now, still I was expecting it to improve faster seeing as I joined the Railroad after Tradecraft taking the name Whisper, I asked whether Dr. Carrington "hated everybody", I did all the relevant bits of Human Error in a way Deacon would like, I was sympathetic to Mr. Abernathy about his daughter and I told Paul to put his gun away during Diamond City Blues - all of which are supposedly interactions he "loves".

I guess I'll keep plugging away and see what happens, still it's a bit of a chore.

I found the ones with easy "likes" like lockpicking and hacking were the easiest, Deacon even likes both. I'd just recommend to go exploring and save main/side quests for followers that are very picky.

I'm playing as a nice/good guy and I got Cait's approval very quickly, which was a surprise since I don't really do much of the stuff she likes (chems, violent approaches, etc).

Both Cait and Hancock like eye-candy. Just be prepared for the comments.