Have a look into the mounting hole library.
The _Pad mounting holes are plated.
If you want it connected to some net, you can either use the conn01x01 symbol to connect the plated mounting hole to any net or you can use the same trick as is used for stitching vias. (give the pad the netname you want with the properties dialog in pcb_new)
If you don't want it connected just place it from within pcb_new and don't edit anything.
To place a footprint from within pcb_new without it being connected to a symbol look in the right toolbar. There is a symbol that looks like a dip footprint. (tooltip: add footprint)