No....those "stop-leaks" won't work on plastic. Believe me ...I'm sure most us here have tried that... I even have an old bottle in my room sittting there...doing nothing.
Your best bet is to go ahead and change the radiator.
I guess you can drive it another couple weeks? Keep watching that spot to see if it grows. And keep premixed cooolant ready in the trunk?
When it's time to change and you'd want to do it yourself, search here and you'll see a lot of write ups...I wrote one even so if don't find any, I help you out.