I guess the issue with that is if the "live pause" spans over more than one programme how would the master box know to add the next programme to record, and so on, and would it then make a mess of the planner with several recordings?
I'm assuming the problem is the mini box doesn't have a HDD but does have it's own cable feed so the live pause is utilising a RAM disk, which is why it can only pause for a few mins.
Sky Q works differently as all the tuners are hosting on the main box. When you live pause, the "stream" from the main box to the mini box is essentially paused and the buffering happens on the main box with the HDD and tuner. This wouldn't work in the Virgin 360 set-up as you would need to stream the tuner from the mini to the master to buffer, and then back again which would struggle over Wi-fi.
As posted previously, if you are going to be away for an extended period then the sensible thing is to just press record and record the programme, which will happen on the main box using its tuners and HDD.