There is a dye intensification process for negatives mentioned in Photographic Facts and Formulas, by E. J. Wall, 1924:

Partially bleach the fixed and washed negatives in:

Potassium Ferricyanide, 0.34 grams
Ammonium Dichromate, 0.068 grams
Glacial Acetic Acid, 8,5 ml
Water, 1000 ml

Then wash, and immerse in:

Victoria Green (Malachite Green) 0.26 gram
Safranin, 0.52 gram
Glacial Acetic acid, 8.5 ml
Water, 1000 ml

Dye for 30 to 120 seconds and wash for 5 minutes.

You can probably substitute Potassium dichromate from a chromium intensifier kit for the ammonium dichromate. You can probably also use indicator stop bath concentrate instead of glacial acetic acid and use twice (17 ml) as much. Dry malachite green and safranin stains can be bought from some biological or chemical supply houses. One that sells to individuals, but has a long lead time on delivery, is elementalscientific.net. I've bought from them, and always got what I ordered, but sometime it takes a couple of months. I think Artcraft will custom order things they don't stock on a quote. A solution of malachite green can be bought at some aquarium stores for treating certain skin infections of fish. The amount to use would have to be determined by trial and error. You might be able to get by with just the green dye without the safranin, which I think is red.

The amount of time to 'partially bleach' the images would have to be determined by trial and error. I have no idea how well this would work with modern films, but it might be a fun experiment.