Australia has a transition layer between A100 and FL110.
To get over the tyrannies of distance the country is divided into areas
here. There is a QNH published for each AREA every 4 hours, on days when there are variations such as a steep pressure front or system passing through an Area QNH may be divided such as North East of a line it's XXXX and south west of that XXYY etc.
The concept is that 5hpa is an acceptable variation. So if we get a terminal QNH more than 5hpa away from the Area QNH we must inform met who review it quickly...
The ATCs have maps on the consoles and often draw lines on screens where QNH divisions happen, when aircraft cross the lines you give them the new A/QNH... VFRs who aren't talking to ATC can operate on departure point or forecast QNH for X miles (I think it's 200) before needing a new A/QNH... They get the new one from an ATIS of a controlled aerodrome nearby, from ATC directly, or from the Area forecast.
No idea how the hold stacks work around here, in Oz most holding is done at high altitudes FL200+... Pretty rare to hold below A100 at the majors anyway.