Yeah, that is why I suggested using them as Death Jesters if you wanted a Harlequin-only theme. From my understanding, the DJ's are really the only ranged support infantry that the Troupe fields, and arming some of them with longrifles wouldn't be too much of a stretch. Stat-wise they aren't too far off from the Dark Reapers. They have lower WS, I, Ld and Sv, but they could be passed off as younger and less-experienced and modeled to show less armor.
If you haven't already, take a look at my custom Harlequin codex (see my signature). It shows my own ideas on what the Harlequins should be like, but more importantly I have a complete list of what I think you could use from the Eldar Codex (or the Dark Eldar Codex) to make a fluffy Harlequin force.