I have been diving long hose configurations for many years.
One of the key parts of doing so successfully is that the long hose is ordinarily breathed from by the donor and is donated to the OOG diver. Simply put, for the the long hose set up to work, the donor needs to be aware of the OOG diver, and be responding before they can attempt to secure a gas supply for themselves. This level of situational awareness is as critical for using a long hose safely as the gear configuration itself.
In order to allow the hose to stow around the light canister, the hose needs to be 7ft (2m) . The original application of this length was to allow OOG divers to be positioned in front of the donor in order to exit restricted passages, but it is also a very nice length when dealing with OOG divers in general.
In terms of deployment, the focus in dealing with an OOG diver must be to supply them with gas as swiftly as possible. Once they have gas, the second step is for the donor to switch to their back up regulator. It is important to stress that this needs to be bungeed in tight under the donors chin. The holder shown in the picture above allows the back up to move about, and can delay access to it. Once both divers have gas, then the donor will deploy the rest of the long hose. It is important to stress that (with some training and practice), this can/must be accomplished with one hand. In a cave environment, one hand is normally used to reference the guideline to ensure a safe exit, but we can apply this to keeping hold of our cameras while we sort out an OOG situation.
I did a GUE Fundamentals class 20 years ago, and despite being a PADI Course Director, a trimix/tech instructor and a qualified rebreather diver at the time I took it, still rate it as the single best diver training experience I have ever had. It is definitely not based around certification, but will put your diving skills and abilities under a microscope. This can be hard on the ego, but is very good for your diving!
I do not always dive in a DIR compliant way, but I use some of the skills and lessons that I learned on the course on every dive that I make!