Right-clicking anywhere, as suggested in that link, does not allow you to change out the isos when asked. I'm sure there's a way to "reload" the .vmx file once you type in the next iso, but I couldn't figure it out.
reminded me of the age-old renaming trick which works fine:
"when the installer asks you to insert the second CD, remove FreeBSD.iso from the C:\ directory and copy the second ISO there. Then, rename the second ISO ("6.0-RELEASE-i386-disc2.iso") to FreeBSD.iso, and press Enter to continue the installation."