Air UK used to do the same out of LHR to GCI.
First on Heralds and later F27.
Front two rows of seats blocked off and mail loaded with nets over the mail.
Row 3 was only used for pax as a last resort as the nets prevented the seat back tables being used.
Worked really well on the Heralds as with row 1 facing aft and having the table between rows 1 & 2 left plenty of space to cram mail bags in
