Our Datamax On-Site Printer
offers the option of printing 4-1/4" x 6" Slotted Fanfold Paper Stock
featuring dual-sided printing; then you fold the stock in half and attach a lanyard with no need for a vinyl holder.
Another idea: rather than trying to print front and back, set up your mail merge to print two inserts side-by-side. The name insert is printed on the left column and the agenda on the right. After printing you simply fold both sides together and slip them into the holder. It takes more paper, but sure saves printing hassles.