I don't see why you can't make a Pan call with the nature of the urgency situation as fuel state just because there is a minimum fuel call layed out in the Jepps and AiP.
Content of PAN PAN Message
2.3.1 The urgency message should consist of as many of the following elements spoken distinctly and if possible, in the following order:
(a) name of station addressed;
(b) identification of the aircraft;
(c) nature of the urgency condition;
(d) intention of the pilot;
(e) present position, level (FL or altitude), and heading; and
(f) any other useful information.
It is not written anywhere that I know of that a Pan call should not be used if the urgency condition is fuel related. The minimum fuel call is not the same as a. Pan call so you can't replace one with the other.