Hi, Remy,
Before I forget this, I "regressed" to 5.2.7 to see if the StartCenter file loading problem I found in 5.3.1.6 was solved. I will have to create some documents to know the current status.
I could not get your idea to work. In fact, I just spent 3-4 hours trying to get your idea and LO's labels feature to work. And it didn't. 
This is what I am trying to do, create a page of labels to fit Avery label #18294.
LO's label creation cannot create a page for Avery letter sized labels, #18294. But neither can MS Word for Mac 2011 and Softmaker Office 2016 for Windows. Printing on the label slowly moves lower on each label and you get closer to the bottom of the page. Or it moves up on the label.
Why does it do this? I think it's because you cannot enter the correct size for the height of the label. In all 3 programs you can only enter .66" or .67" for the height. But neither number is correct. The actual size of the label is two-thirds of an inch, a repeating decimal to infinity, I.E. .66666666666666666 with 6's going on forever. So, if the programmers formulas for calculating height is limited to 2 decimal places, there is no option but to have a built-in error.
It had been suggested to me, somewhere, to use a table. And that's where the problem of the extra line feed, that is unnecessary if you change the program code, comes into play.
And you end up screwing around and wasting your time with all the various workarounds.
Anyway, I created a frame, and sized it to fit the page margins I had set up. Those margins were the ones that should fit the area of the sheet of labels I wish to print. Then, I created a table inside the frame.
I was never able to get the column widths to be correct. In the Table Properties, I typed in the exact dimensions of the for the columns, had all the text offsets I could find set to 0", and then LO would simply change the widths to whatever when I exited the dialogue.
So I went to the Avery website, downloaded and installed their Design and Print software. In 10-15 minutes, I had a page of labels that fit.
From now on, it's the Avery software for me, when it comes to labels. I am going to install the current version of Open Office, see if it has the same problems. 