Hide Sender Address from Label
Joovii Shipping
Hiding the Sender Address from a label is possible in Joovii Apps, although does increase the chance of slower or missing parcels in a Return to Sender situation.
For Joovii Shipping account users, the Hide Sender address can be found in the Account settings. It must be set for each carrier (Aramex and Couriers Please) by pressing on the Cog symbol:

Then making this selection:

Note that this masks the Sender Address, you cannot set an alternate address like a PO box as a genuine pickup address is needed to collect the parcel.
Aramex Accounts
For merchants with their own Aramex account this must be done in Aramex Connect.
The setting can be found in Administration > Settings > Label

For Auspost there is no way to hide the sender however any Sender address may be added given that the parcels are dropped off rather than picked up.