If you still had it in your possession, you would have two options. You could try artificially hibernating it your self, or gradually warming it up and get it active for the winter. In both cases, I don't see why you can't release it in the spring as long to make a strong effort not to cross contaminate with any other animals in your collection.
To hibernate it your self, use a shoe box filled with moist coconut fiber and place it in a room that is attached to the house and will not freeze, but is unheated. Garages are ideal. Otherwise gradually warm it up and set it up in a ten gallon with coconut fiber and hide spots>>> with a heavy lid! I would imagine that their captive care is similar to American and Fowler's toads. Thanks for picking it up and taking care of it!!!
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...the oldest task in human history: to live on a piece of land without spoiling it."
Aldo Leopold (1938)
"Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us."
Calvin and Hobbes (Scientific Progress Goes 'Boink', 1991)