In "Part Un", I blogged about a trivial but cool addition to my MFT-1080 that allows me to quickly get repeatable measured cuts on the off-cut side of the guide. Thing is, this grand addition partly assumed you did the modification I did to add 4 1/2" of crosscut capacity to the MFT-1080. Not everybody did that. Shame on both of you. :) Voilà, here, I'll show you how to create that handy detachable fence for use with the original MFT fence.
Measure the width of the extra fence you have; mine's about 35mm. Mine is a Festool replacement from the EKAT system; read Part Un for details. Note that it doesn't have to be a Festool fence; anything you can attach from behind will work although I had this and it uses the flag stop :)
Subtract the width of the fence from the distance in step 1. (17mm for me)
Subtract an extra 3mm (1/8"). (14mm for me)
The resulting measurement is the distance you want your block to be from that parallel row of holes. Mark the face you have facing those holes; it will face the fence.
Afterwards, push in two pieces of 3/4" dowel and glue in place. This should be a snug it to the MFT top.