I have looked at mine and it looks like it would be hard to reach the seat catch arm from behind as the seat drops down over that black plastic housing covering the operating arm. However the seat catch arm is pulled by the cable from the left so if you push away the mesh plate over the RIGHT fake air vent you might be able to push it open with a screwdriver?
Push the mesh plate away where it's fixing posts are at the front and rear top and bottom - it is held by spring washers over the plastic posts - even if they break off you could glue it back in place
(1) position of seat catch arm[You must be registered and logged in to see this image.]
(2) distance from RIGHT rear air vent to back of seat catch arm & the right angle to push[You must be registered and logged in to see this image.]
I previoiusly posted a picture showing a screwdriver in pushing position but it was wrong! The catch arm will arc across then forwards so you need to push it from as far back as possible to keep purchase on it
I hope that works