This is the first I have heard of a 'minimum' level. If there were one, I expect it would be found in the standards of the local PoCo.
PoCo standards are not binding when the park does its' own billing.
"Standard" Service pedestals seem to place the meter at about the 4-ft. level. Such pedestals have, as part of their base, an accessible trough that extends into the ground. I would expect that you can splice the wires in that trough, to reach where you must.
How to splice? My first choice would be crimps, wrapped in tape and covered with Scotchkote. NSI's Polaris connectors would be my next choice, similarly sealed with Scotchkote.