I’ve recently been in the same position as the OP and booked a positioning flight with EI from MAN to DUB to catch a well priced WTP flight via LHR.

My flight’s in a few weeks but from previous experience of transiting through DUB it’s fairly easy.

My only gripe is that when booking directly with EI and even putting the BAEC number into the booking it’s not possible to select seats ahead of OLCI for free.