Fan Fixing

I've been using a 100mm PC fan to vent my (wardrobe) grow space, and so far it's worked really well. However, the one drawback is the appalling funk that now pervades every room in the house. Its got to the point where you can tell if your visitor turns on or not just by the initial expression on their face when you open the door and the green miasma hits them- needless to say, the Filth Avon Ladies & Witnesses get no response to their knocking.
Anyway, I've now obtained a 100mm carbon filter and I'm assuming that the extraction will have to be beefed up to cope (Unless someone knows better?). Not having the wherewithall for a RUK I'm looking at using one of those in-line fans used in bathrooms- their cfm and dB specs seem adequate. Unfortunately I've hit upon a couple of snags. I'd like to be able to use one of the sort where the fan is mounted onto a vent grille. It could then be fitted with the grille on the outside of the wardrobe making for a neat installation. Unfortunately though that would then work in reverse of whats needed ie. the airflow would be INTO the growspace and OUT through the filter. Therefore I'd just like to know if these fans can be wired to run in reverse? If not i will just have to use a "remote" fan with connections for ducting on both ends.
My other point concerns the fact that most of these fans incorporate a timer, and I'd just like to know how simple it is to override the circuitry to enable continuous running. I can use a soldering iron so hopefully it wouldn't be too much of a challenge but hopefully someone out there can enlighten me? thanx.