Sure, I use my old Play 5 Gen 1 speakers just that way since Sonos bricked the electronics during the early upgrade program.

Open the Play 3 up, remove all the electronics. Add a crossover and speaker connectors to the case. Seal it back up.

First hit, something far smaller would work better for your Play 3:

https://www.amazon.com/gp/product/B016FBNNCY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

https://www.amazon.com/Terminal-Binding-Amplifier-Insulated-Connector/dp/B0D4TBVPCB/ref=sr_1_1_sspa

Stanley_4, thank you so much.  I thought about opening up the Play 3, but would not have known what to do next.  Is the installation of the crossover and connectors intuitive?  In other words, will it be obvious where/how to install?  My AV tech experience is extremely limited.  Thanks again for the advice.

The Play 5 was pretty easy to figure out, the crossover is marked for woofer and tweeter so the only thing to watch is getting the plus and minus terminals matched.

Not great but it should give you an idea on the innards.

Got it, Stanley_4.  Thanks again.  Your info very helpful.  I was able to remove all the innards and connect speaker wires to the speakers, running them out through the power hole in the back.  I now have a useable speaker for my old turntable, and the sound is quite nice.  

Glad it worked for you, I’m really happy with my gutted and repurposed Play 5s too.