Docker agent template image supporting jenkins environment variables?

[pgaucherand]

Hi,

I have tried to specify a custom docker image at run time for a particular docker agent template.
The particular use case I have in mind would be to specify an image as follows:
<image_name>:$BUILD_NUMBER
However, there is no variable substitution performed.

I guess the question I have is: is there particular technical limitation as why this can't be achieved?