Put in the tags the names of a female idol and a male idol, most of the results will get you straight fanfics :). I also notice that the "romance" tag is more often used in straight stories than gay ones, the gay ones typically only use "" since it implies romance between the characters^^
There's currently a male-idol x oc recs list featured on the front page, so maybe start with that? (If you enjoy EXO, that is - if you don't, then you might have to hunt a bit.)