Once you create the PO's you have a couple options.
If you go to create a check to the vendor and the PO's are still open, it should pop out a flyout where you can add all the PO's onto 1 check. (see picture)
The other option is for each PO, you can convert it to a bill. Then go to the Pay Bills menu and you can check mark all the bills for that vendor and it will combine them onto 1 payment check.