Beer from leftovers

I've got 4 pounds of extract leftover and a couple ounces of hops. I'm gonna make some invert sugar and make a 4%ish brew.

My problem however is I don't have any yeast laying around and the beer store is closed.

I do however have an English Ale using WPL002, another using Nottingham (both in bottles), and a Belgian 1 week into fermentation using WPL500.

I don't want to take any yeast away from the Belgian, but that is certainly an option, so my plan is to take the trub from a couple of bottles of the English stuff.

What's my best option here to ensure the health of this yeast? Keep in mind I only have 4 pounds of extract to work with.

i would definitely make a small starter by pouring the bottoms of a few of the bottles into a starter around 1.040...and if you can i would step it up. If your trying to do this today without a starter your probably going to need more than a few bottles, decant the liquid and just use the yeast but i would use the starter.
https://www.homebrewtalk.com/f39/starter-question-using-lme-53277/