youre only hope is with agar.
most certainly you will need to transfer
more than once to fresh plates.If they are cubensis you could take it from there.
Try scraping just little bits from the bottom of the cap onto agar. On multiple locations on your plates.
Something should germinate most definately amongst contams. If you are lucky VERY lucky
you'll get a few germination spots that are not touching contams. move these onto fresh agar etc...
I'm pulling this out of you know were but it is the most logical procedure I can think of for you to propagate.
Good luck,
post any results.
greco