While I appreciate that you are not able to drill holes in the property so running "normal" Ethernet cable through the wall is ruled out but you can get flat Ethernet cable which you can run under the cupboard door and along the skirting either under the carpet or stuck to the skirting board with double sided tape which would not damage anything and is easily removed if required.
If you can run this you could run it to either a wireless access point near to where you use your devices which would allow a wifi connection or to an Ethernet switch where could could connect your devices by Ethernet if they have Ethernet ports.
Alternatively you could run the "flat" Ethernet cable from the ONT socket which the BT hub is presently plugged into in the same way as above and move the BT hub to where you want it use it.
Unless the landlord is in the same property and can see what you have done , how would he know you have moved it and in the event he found out you just put things back to how they are and remove the double sided tape.
