[Freesurfer] Creating DLPFC label

Hello!

I am attempting to create a DLPFC ROI, based on methods described in : Yendiki et al. (2010). Multi-site characterization of an fMRI working memory paradigm: Reliability ofactivation indices. Neuroimage. 53 (1), 119-131.

Those authors state they merged existing parcellation labels, and then made a "coronal cut at Talairach coordinate y=26." I have successfully merged the existing labels, but am having trouble figuring out a good way to do the cut. I have tried using the "Make closed path" and "Custom fill" options in tksurfer, but am having trouble getting those to make a clean cut right at y=26.

I'd appreciate any suggestions!

Thank you, Allison