The porous clay watering systems that I've seen include an attachment that you use for a drinking bottle to automatically fill, so I'm not positive these are the same that you're referring to. However, this will release quite a bit of water for a cactus and wouldn't last for 2 months (mine is usually empty after a week, so my fast drinking plant can last about 2 weeks without me).
A simple DIY solution is to place one container of water above the plant and leave a piece of string or fabric running from the container down to the cactus. The string will slowly wick the water down.
There are also electronic systems that may give you more control, though they are expensive (e.g. this one over on Amazon.
No matter which solution you use, test it long before you leave so you can be sure there are no leaks, and should it over waters things, you're around to stop it.