Use Titanium Backup!
Load Titanium Backup, wipe the PK app data then change the andoid ID.
Load pk, and make another account. play as much as you want, make huts, wells etc.
Exit pk, load Titanium backup again, wipe, and change anddoid id again.
Make sure you set the harvest cost to 0 or what ever you want, and give your main passage.
Do this as many time as you like, then wipe and change a last time and use you main account.
Now go tend your crystal farm!