Although the above product is a ready to go solution, after building my own version there are a few problems with its design. For starters the Canon sensor is tiny in comparison to a sheet of 4x5 film or even 6x4.5 which the tech camera was designed for, so you have to use the lens standard fairly close to the sensor to achieve focus. On a DSLR the sensor is already buried deep within the camera, then having the camera mounted onto an extension tube puts the sensor even further from the rear standard plane, severely limiting the use of tilt & swing, the front and rear standards will have to be very close together leaving little room for movement. The other problem with the extension tube design is that the image circle cast from the lens will start to create a shadow onto the sensor with only a small amount of movement, due to the small size of the sensor and the fact it is sitting down the end of a tunnel so to speak.
Here's an image showing how I made my bag bellows and camera mount to keep the sensor as "exposed" as possible -
Also I wouldn't trust mounting my camera and having it hang of the lens mount, especially not from a cheap 3rd party extension tube, recipe for dead camera...