Bloomin' Fabia vents

As many know I've been running a boost gauge in a knackered vent slot in my mongrel. Well, now the gauge has moved north about 6" I felt it time to replace the vent. Had specially bought a single driver's side vent off Ebay, with the plan of removing the internal bit and shoving it in the centre vent.... (twiddly bits on the correct side)

Just came to change it this evening.... bugger! The vent unit is about 1" shorter than the centre ones, so it doesn't fit! I've had this bloody thing lying about for about a year now Anyone want to swap it for a left hand centre vent bit?