Sorry for a response after a long time. I finally managed to find out a way to commute from LRT/Buendia to Ayala Manila Bay (and back).
There are buses going to PITX passing by LRT/Buendia (and vice versa). You are dropped off near the commuter terminal area of the mall, and when going back, just cross the street at the intersection to catch a bus going the other way.
I hope this helps any other commuter with a similar problem.