I guess I didn't understand this post. What I suggested avoids may I questions and opinions.Why old son?
When it is a single disconnect it is allowed to be in the same cabinet with the breakers it supplies. A back fed breaker with a tie down should work.
I believe that the 2020 requires that the conductors and terminal lugs supplying a Service Disconnecting Means breaker may not share a wiring compartment with any of the breakers it supplies. But that may only apply to exposed busbars and terminals The idea is that there has to be a way to deenergize the entire wiring compartment so that it never has to be worked hot. With a single enclosed double pole breaker that has the new non conductive terminal guards on the Service Entry Conductor termination lugs above your panel You can work in that enclosure with no exposed energized conductors, terminals nor busbars. When you open that breaker then everything in your small panel is deenergized and you don't have to work anything hot. Their is a strong push on from the workman's compensation insurance industry, OSHA, And the electrical industry as a whole to put an end to working hot on any kind of routine tasks.
You could still run the service conductors into the terminal lugs of an appropriately sized double pole breaker and install it using a tie down kit so it could not be removed from the busbar accidentally or from ignorance while energized. I believe that the 2020 edition no longer permits exposed busbars, terminals, or other energized parts to be controlled by a breaker in the same cabinet as the portions of the panel it supplies unless it's supply terminals are in a separate compartment. With a single disconnecting means the inspector may except the terminal lugs of the main breaker as suitably guarded. Is the panel marked as "Suitable for use as service equipment?" If the inspector will except a back fed breaker with a tie down as the Service Disconnecting Means then you should be OK to run the energized service entry conductors into the terminal lugs of a tied down breaker. That will supply the busbars through the tied down breaker's busbar stab clamps and once it was opened it would deenergize everything else in the panel. If the panel is marked as suitable for use as service equipment that would do the job. You would then have to add the breakers for your individual loads.
Since when did common sense override the "rules"?Maybe not where you're at, but temp poles here are set up and treated just as I described. I don't get applying the new 2020 rule for a disconnect ahead of the service to a temp pole/service. The disconnect is mainly for the fire department to shut off all the power. You don't exactly need to have the fire department for a temp service. It's usually one or two workers plugging in their tools. You're not powering a house!