Try citrate-phosphate for an amine-free low-pH elution buffer

http://www.sigmaaldrich.com/life-science/core-bioreagents/biological-buffers/learning-center/buffer-reference-center.html#citric

Thanks for the suggestion Adam.  Unfortunately, our purification team has explored citrate-phosphate but I have been told the yield was unacceptably low compared to Glycine/Tris.

Have you tried high-salt elution?

To the best of my knowledge they have not explored high salt-low pH elution with citrate.