Nizo: tripod mounts
Many of the Nizo Silberling types, such as the Nizo 801 and Nizo 801 Macro, have a 1/4" tripod screw hole hidden under the bottom plate where the battery contact points are (at the front near the trigger). You can take the plate off and drill a hole to allow access to the tripod mount.
Since the batteries in the handgrip do not make contact when you fold the grip, you will need to use an external powersupply. Nizo used to offer a tripod kit with a drilled plate and a short power cord to connect the handgrip batteries while it is swung back and sometimes these cords turn up on eBay.