For anyone who wants to do this without termux, you can use connectbot to execute a pre-compiled binary that you, for example, compiled on ubuntu or downloaded directly from rclone.org.
https://beta.rclone.org/rclone-beta-latest-linux-arm.zip
I didn't realize we could use the connectbot data directory to execute stuff. Simply open a local connection in connectbot
cp <rclonebinary> /data/data/org.connectbot/files/
chmod 755 /data/data/org.connectbot/files/<rclonebinary>
/data/data/org.connectbot/files/<rclonebinary> serve --config=<configpath> remote:
Also see this thread. Pretty nifty:
And this issue which will make this even better: