Yes, this way to solve it is possible. But it comes with a warning: These customized UOM is only valid for these specific products. You run a risk that they might be used by mistake on other products. And then you run into problems.
Since you purchase all in volume (L and Gal), my recommendation would have been to also use volume in BOM. And then take the effort to calculate gram (I guess that is the recipe) into L / dl . If you stick to ISO units, the risk of mistakes are reduced.

Hi Lars, thank you for your response. I would love to be able to do this, but not all of the gallons I order have the same density. Therefore, I would be unable to use the standard UoM on all of them, across the board. However, I have made sure to label the UoM's to correspond with the product, so there is no confusion at all. Thank you very much for your feedback.