Maybe BA Cityflyer with their E170s might be able to tempt Dundonians away from using EDI? They offer the best connections at LCY plus Avios points.
The E170 would almost certainly be more appealing than the D328. Apart from anything, Dundonians are more likely to notice a BA E170 with its striking livery and traditional twin jet profile flying in and out of their local airport than the rather nondescript and antiquated D328 which has a size, appearance and livery which probably leads any Dundonians who might happen to notice it to believe it is probably a private aircraft.
It would be a big gamble though given the lack of patronage for the existing and previous services from Dundee. Maybe if HIAL gave BA Cityflyer reduced or free landing charges for a time to try to get the service up and running and if the local newspapers, Chamber of Commerce and other business organisations gave it one last big push it could be made to work. I have my doubts though. Dundee Airport is just too close to EDI.