Minnflyer's suggestion is probably the easiest.

A (radical) alternative is to cut the wire joiner using a Dremel tool creating independent elevator halves, and installing either (a) a split linkage to a common servo, or (b) using a separate servo for each elevator half. There are advantages and disadvantages to each - and a lot more work, expecially on a covered fuselage.

I'd try Minnflyer's idea first.