Hi, welcome to the Apple Users Community.
My advice would be don't try that any more. Borderless printing is a waste of ink and time. It only over-sprays the edge of the media and causes issues with build up inside your printer over time. Of course Epson told you its not an option because they can hardly provide you with a working option that actively makes your printer inoperable over time.
The only way around this to use over sized sheets from your desired finished piece and cut down after. RA5 is an oversized A5 sheet and SRA5 is even bigger that RA5. A good self-healing cutting mat is a great help as a printout of a measuring tape to go underneath the mat and a thick metal straight edge, to cut against. A good supply of cutting blades, I use an OLFA L-2 with snap off ends interchangeable blades.
If you need any more help with sheet sizes just reach out here again.
Best of luck