Hi,
You may try to connect to a custom attribute (eg: offset ) instead directly to other object's .tx, .ty, .tz. and then connect this "offset" to .tx, .ty and .tz using expression or however you want it to.
This would feed this offset to translations or rotations, whatever u will be using and will offset the value with the value of this custom attribute.
Hope this helps.
Cheers,
Amit