I am sure there is an easier way.
Imagine some 737 from Dublin to Gatwick.
Is there a little Irishman, going through the passenger names and their addresses and passport numbers, and faxing off GAR forms to the appropriate special branch fax numbers?
Yeah, right
The back end system for this is already in place and has been for many years. The website would merely need to stuff the data into it.
The way to approach this would be to establish contact with the Home Office and prod them into doing this. Every single airline must know about this system - they do it every day.