Could you use a floating thermometer as a hydrometer? Check it in another homebrew- let it go flat first. Then compare float level in degrees between the 2 brews? It won't be exact, but could compare between the two.
But then 3 weeks in secondary shoulda done it....
So far, I've had more experience thinking than I've had brewing....you don't think they are mutually exclusive, do you?
72 batches so far,
48 wine, mostly Loquat, peach, plum, prickly pear
23 beers and ciders
1 Tequila, from a prickly pear wine experiment that didn't work. I call it "Prickly Heat"