It's a cryin' shame Lucifer doesn't have access to his healing capabilities (though that would be added to the rank of Greatest Joke Against Lucifer if he did have that instead of, say, his barely-there smiting capabilities), because that could... open up more, ah, unconventional means.

But he is satisfied with Istredd's answer.

Then your mind's played it too safe. "Take the big risks, find the thrill!" Of your imagination? Whatever. He tosses a piercing look over his shoulder as they walk, all the lilt gone from his voice as he points out, "Though you did take that first, big risk. That leap." In trying, in potentially risking their friendship and putting them completely into unknown territory.

It's a weird credit to give but Istredd should get it, anyway.

(It's also far better than Lucifer saying 'aw, you're adorable' because Istredd's already a touch embarrassed and it comes too close to laughing at Istredd, which would not be his actual intention.)