Yes, you can if the following conditions can be met. You must have enough room in the NID to install the in-line filter and you must have a way of connecting the in-line filter to your home run.
*Disclaimer: Microfilters are not designed to be used outside while exposed to the moisture and temperature extremes seen within a NID. Microfilters are NOT recommended as a permanent solution and should be replaced with a proper splitter!*
To complete this task, you will need the following:
An inline filter, such as the Excelsus Z-Blocker Z-D250TJ, that is provided in the FastAccess self install kit and a modular plug such as a Radio Shack model 279-383. As an alternative to using the RS plug, you can also use one of the mounting cords from a spare in-line filter by cutting off one of the modular plugs, stripping back the jacket and then using ScotchLoc connectors, connect the red and green wires of the mounting cord to the white/blue blue/white pair of your home run, as follows: red to blue/white and green to white/blue. ScotchLoc connectors can be purchased at most home improvement stores. Radio Shack also sells an off-brand of the ScotchLoc connector. The model number is 64-3080.
Open up the NID and locate the entrance bridge network (EBN) for your ADSL line. The EBN is the device with a modular plug inserted into a modular jack used for testing your line. Unplug the modular plug from the EBN and insert it into the jack on the in-line filter marked phone. Then attach the RS modular plug to the blue/white white/blue pair of your homerun and plug that into the jack marked DSL/HPN. Finally, plug the mounting cord on the in-line filter into the jack on the EBN. Close up the NID and youre done.
Photo by HamRadioNut.
Schematic by Andy Houtz.