So there is nothing currently in the game that lets you do this. If this is a modding question there is a modding forum
here.
However while I'm here I'll take a whack at answering your question.
I am going to assume that you have some understanding how Reactions work and some basic modding knowledge so I'll get right to the point of it. Secondly, I'm doing this off the top of my head, so if this doesn't work let me know.
You need two things, you need a reagent with the container, and a reagent with the liquid. Here is the reagent of a container
[REAGENT:container:1:NONE:NONE:NONE:NONE]
[CONTAINS:extract]
[PRESERVE_REAGENT]
[DOES_NOT_DETERMINE_PRODUCT_AMOUNT]
I opened up reaction_other.txt and copied a part of MAKE_SOAP_FROM_TALLOW and modified the names
Now that we have that you need to define the extract. I think the easiest way to do this would be through a REACTION_CLASS. With this tag you can group materials into REACTION_CLASS and then have the reaction call any material with that class. Make sense?
[REAGENT:extract:1:LIQUID_MISC:NONE:NONE:NONE][REACTION_CLASS:GNOMEBLIGHT]
This reagent will take 1 of any LIQUID_MISC with the reaction class GNOMEBLIGHT. All you have to do is open up your plant raws, find the block of code that talks about gnomeblight, and then paste [REACTION_CLASS:GNOMEBLIGHT] at the end of it.
You can name reaction classes whatever you want, they are quite versatile as far as modding goes. So if you wanted to use a different extract, just duplicate the reaction and change GNOMEBLIGHT to LIQUID_FIRE and paste a reaction class into liquid fire.