SoCo lets you access the current playing track - this example will get the URI (Change the IP address to the zone player that is a master playing the track)
import soco
zone = soco.SoCo('192.168.1.72')
print(zone.get_current_track_info()['uri'])
You can then use the uri to play a stream from spotify with a seek to 15 seconds in and play for 10 secs:
import soco
import time
zone = soco.SoCo('192.168.1.72')
zone.play_uri('x-sonos-spotify:spotify%3atrack%3a45yEy5WJywhJ3sDI28ajTm?sid=9&flags=8224&sn=7', start=False)
zone.seek('00:00:15')
zone.play()
time.sleep(10)
zone.stop()
I think that answers your question, but you will note that the Sonos controller shows the uri as the title etc. as meta data is missing.
I guess what you really want to do is to browse Spotify and pull out the tracks you want then add them to a queue to play - even if only 10 seconds of.
The interface to music services is still work in progress on SoCo see https://github.com/SoCo/SoCo/pull/412 great work by Kenneth Nielsen.
Hope this helps - feel free to ask more here or on the SoCo issues page on github.
Cheers David