[Steve in Chicago]

Like stated above, you can get the retention parts that fit into the OEM mat and install them into a mat of your choosing. You'd need to cut the proper size holes in the proper places on your replacement mat. You may also be able to reuse the plastic hardware from your old worn out mats.

http://www.ecstuning.com/Volkswagen-Passat_B5-FWD-1.8T/Interior/Floor_Mats/Hardware/