Best way to define units for DynamicQuantities in a Pluto notebook

[alhirzel]

The package DynamicQuantities.jl allows a user to define custom units:

@register_unit lbf 4.4482u"N"   # allows you to write things like 10u"lbf"

It is sensible that this "custom" namespace of units isn't monitored by Pluto: how could Pluto possibly out-craft all the crafty fox macro writers of the world? Having understood this, what is the best way to make sure the definition above occurs before u"lbf" is used? Is there any way to tag the cell containing the invocation of @register_unit as the defining cell for u"lbf" or something like that? I read briefly about some macro analysis that Pluto performs; is there some kind of heuristic cat-and-mouse trick I can PR an improvement against?

(Note that this question is similar to #1374, but DynamicQuantities.jl does not require the same module shenanigans mentioned in that discussion.)