How to Trendline using a Single Select Slicer

Good morning. 

I am building an executive dashboard at the moment with some very specific requirements. There are definitely nicer ways to do this, but for the requirements I have, I need a particular solution. 

I am using the KPI visual which gives a nice number and trend. Happy days. 

What I want to do is have a single select slicer for month-ends that allows a user to see what the number was in a previous month. That's easy, but I want the trend in the visual to display the 12 months trend up to the date in the slicer.

I know I can have a slicer for between dates (and that may be all I can do) but given the report is all about month-ends, I don't want users to mess about with a slicer that has every date in-between. It would be much cleaner if they can select from a slicer that looks like this:

This would give me the value for the 31/12/2021 in the card, and the trend would show data for 31/12/2020 - 31/12/2021.

Is this possible? Am I missing something obvious?