shoyu stains in textiles?

ahoy everyone, i dropped a bottle of dark soy sauce in the kitchen, of course it broke and splattered everything, including my pants! my normal detergent doesn't get soy sauce stains out (i know that from my kitchen towels). are there any grandmother tricks for getting rid of soy sauce stains in textiles, like with red wine or grass? if not, i'll just have to buy some kind of commercial oxi-wash product, i guess.. any ideas? i can't bleach these pants.. rehfilet