Retrofitting one-touch electric window
The GTi and some TZ trim level diesels have a four-function window regulator switch on the driver's door: regular up and down while you push the button, plus an automatic up and down to the appropriate end position with a single push of the button). It is easy to retrofit this unit to another model with simpler electric lifters: go to a salvage yard and find a GTi or TZx with this unit fitted. Remove the door trim panel and separate the secondary panel housing the window regulator switches. You'll need the four-function switch (in contrast to the simpler switch, this has a middle section with the two arrows pointing up and down, plus two outer buttons with a circle marking). The wiring harness starting from this switch goes to a relay unit in the door, then from the unit to the white connector near the bottom of the door (near the radio speaker) plus the other wiring harness connecting the other (passenger's side) switch to the brown connector at the bottom. In your car, you have to swap the regulator switch, the wiring harness and fit the relay unit with three small screws (its place is already there). That's all.
Christian ULBRICH confirmed that the same unit can be found in some CXs and can also be used but due to the different layout inside the CX door the cabling is shorter than necessary for the BX, thus a little soldering will be required.