Make the exocrines move, so deploy a full unit of reapers just out of range, just in case they seize.
Prepare for the deep strike, Farseer+reapers+Forwarned = dead or gravely wounded DS unit. Have a screening unit ready to absorb the DS charge just in case.
A concealseer is also nice to drop on to the reapers, minus 2 to hit will mean you only have to seriously wound the exocrines instead of out right killing them.
Basically castle up, only give him the ability to hit the things you want him to, and account for consolidation when deploying.
Harlies with a Troupe Master are fantastic in close combat, screw the fusion pistol, you've got CWE to bring in the high Strength weapons, save the points and use the harlies as counter assault units, you know your going to get charged from DS anyway. Just be sure to focus on a single unit, morale generally isn't an issue for a well built Nid list.
Part of me thinks you might be better off running them as Ynnari, you want reapers to be raining down as much as possible and triggering extra fighting for Harlies is also a nice option.