[CONNECT C++] How do I stop an EC area formatter appending a unit decorator?

Here's what I do to create an area formatter corresponding to the Mstn Property Formatter schema...

WCharCP                 AreaClassName           { L"AreaClass" };
ECN::ECClassCP          formatClass             { formatSchema->GetClassCP (AreaClassName) };
StandaloneECEnablerP    enabler                 { formatClass->GetDefaultStandaloneEnabler () };
StandaloneECInstancePtr localInstance           { enabler->CreateInstance () };
WCharCP                 PropUnitDecorator       { L"UnitDecorator"	};
ECValue                 valDecorator            { decorator };
localInstance->SetValue (PropUnitDecorator, valDecorator);

This works fine — I get an area formatted something like 10 Sq. m or 10 m2.  But how do I prevent the formatter from appending that decorator?  I want to append my own decorator, using engineering format, so it looks like 10m².