Using fx: constant in attributes?

I am wondering if it is possible to somehow use <fx:constant>an attribute instead of a separate tag?

This currently works for me:

<Label>
    <text>
        <MyController fx:constant="MY_CONSTANT_STRING" />
    </text>
</Label>

while I would prefer something like this:

<Label text="<MyController fx:constant="MY_CONSTANT_STRING" />" /> 

Something like a later one?

Thanks for any hint!