Malt is malt, pilsner is just lightly kilned 2-row. Where are you reading that pilsner malt wouldn’t be appropriate? I say go for it, should be really tasty!
By lager malt, do you mean pilsner? Lager malt isn’t really a thing, it’s just malts that might get used in a lager, which could be any kind of malt you could imagine. 20% pilsner malt would be fine with a 60 minute boil as long as it’s well modified. With a good hard boil you shouldn’t get any DMS. If you’re going 70 minutes, you’re golden.
I’d probably go with 100% pilsner malt. That nutty grainy taste you get from a good pilsner malt probably wouldn’t come through at just 20%. A nice light blonde ale with some American hops and pilsner malt on a hot day? Yum!
Its actually my Smokin’ Hot Blonde jalapeño ale. Originally it was a bastard cream ale recipe that I took the Pilsner malt out of and added wheat. The three of us that had the original recipe vs the revised one all felt the previous one was much better. I liked the name though and wanted to keep it. Funny as I don’t name my beers.