I think it would work! And in the folk tradition vasta is also used for herbal medicine.

Nettles and juniper need to be first soaked in hot water to make them less stinging. And of course it is also possible to make bundles of smaller plants, for example you could have one cooling down the forehead, and another one filtering the air to breathe.

EDIT: Forgot to mention; if you try this, place a bucket of cold water so that it easy to reach. For the vasta will get warm sooner instead of later, so that you need to keep on "recharging" the cooling effect by dipping the vasta in cold water by regular intervals.