You can simply hold the shaft in your hand, or put it in a rod holder!
This particular rod holder in the photo is simply stuck on with velcro to avoid drilling into the kayak itself. The drill battery will rest on the kayak in most cases to achieve the correct shaft angle, so there is very little weight on the rod holder either way.
You will find it’s actually easier with NO rod holder… as you can rest the shaft on the kayak or boat transom and move the Water Glider to the side for easy turns. This is a good idea if you are using the kayak to get to a vessel or somewhere you can put the Water Glider down safely without getting your drill wet.
If you are going fishing, then a rod holder would work better to rest the shaft and drill in while your not using it. The drill handle diameter is only 32mm, so it will slot into just about any stock standard rod holder.