abutment ventilation

i have had a mono pitched roof built on a ground floor extrenson. approx 3m wide by 2m deep. it has in it 2 big velux windows. there is a 10m venting strip by the fascia at the bottom but no abutment ventilation has been put in at the top. there are 7 7in roof spars that divide the roof. problem is where the roof joints upto the house wall the lead flashing sits under a bedroom window with almost no depth for an abutment vent.
does anyone know of a retrospective solution? one thing i have come across is a klober uni-plain tile vent - dont know what people think of that?
any offers appreciated.

There are some discreet roof space vents that are designed to correspond with common tile types and colours. Use two or three of these near the top.

Next time use breathable roofing membrane.