I have an LG UW monitor daisy-chained behind a P2415Q.
- Make sure your computer/GPU supports DP1.2 (e.g. the HD4000 in the 2012 mini does not).
- Set both displays to 30Hz(!) in the monitor settings on your computer.
- Set the first monitor in the daisy-chain to “MST Primary” and the second monitor to “MST Secondary” (Monitor menu “Display” -> “MST”). There is also a hotkey for this setting (See this Dell Support document for details).
- If need be, power cycle both monitors for 15s (had to do on mine).
I’m not sure if it needs to be exactly 30Hz or if 29Hz would do as well (can’t check, as I’m far away from my setup currently), but seem to remember that having 29Hz on the LG caused problems.
You may still want to stay with having both TB ports used, though, as daisy-chaining only allows for 30Hz on those monitors, which is a bit on the sluggish side, depending on the amount of mouse action / general movement happening on screen.