As chrfr said above, some drives have both Firewire and USB ports, but they're uncommon (especially these days) and more expensive. It's unlikely that you have these.
Unfortunately, there is no reasonable way to convert any of your three remaining "ports" (Firewire, Ethernet, SD card) into USB. While Firewire and NAS (Ethernet) drives exist, they are more expensive and, in the case of Firewire, more difficulty to find. At the end of the day, even if you had functioning USB ports, you're dealing with USB 2 on this MBP. Any drive access is going to be noticeably slow.
To circle back to your original problem, how do you know the USB ports are fried? Have you tried an SMC and NVRAM reset?
Update!
First, to answer your question, no, I just took the seller's word that
"the USB ports no longer worked", and when the computer arrived, I inspected the ports and saw one of the ports (left one) had something like stardust residue inside it, (I thought probably from some frying incident?) Although there was no indication of spark's burn (or any discoloration, as one would expect) around or inside the port. Nothing responds when connected to this left port.
The other one however (right one) is fully responsive when connecting a mouse.
However, when something more "heavyweight" is connected, like an external HD, I immediately get a pop up notification:
"
USB devices disabled - unplug the device using too much power to re-enable USB devices"
https://support.apple.com/library/c...-sierra-notification-usb-devices-disabled.jpg
I have no idea why I get this message (Could it be that the aforementioned frying incident left this other port
"kinda" damaged? Don't know, as I'm not tech proficient.)
Even though I get this message, the HD seems to have Time Machine working properly. Don't know if I could trust it not being corrupted though, given the condition of the port.
Also, tried plugging the HD while the computer was turned OFF. I did, and then turned it ON, and I didn't get the "USB devices disabled" notification
at all. TM also seemed to work ok, but again, don't know if I can trust the HD not being corrupt when plugging it to another computer.
Also, yes, I tried the SMC/NVRAM reset method. The exact same thing happens. Left port completely unresponsive. Right one gives me the same pop up notification, (unless I plug the HD before turning the computer ON)
Thanks.