Not without reencoding, since the MKV doesn’t have the letterboxing bars required to get the vertical resolution to the required 720 pixels.

You’ll either need to use a Blu-Ray compliant h264 encoder and decent compression settings to reencode it while adding letterboxing, the output of which you can then remux using something like tsmuxer to make a BDMV folder or ISO image to burn to disc, or use a full-on Blu-Ray authoring program to do it all at once, but those tend to be limited on encoding options, leading to stuff like pixelation.

It’s something I haven’t toyed with in a while since I watch most of my stuff on my media player through rips I make of Blu-Rays I own rather than putting a disc in a player, so I don’t often burn fan projects to disc anyway.

Someone else will probably have more specific suggestions for you, but if I remember after work tonight or this weekend at some point I’ll do some Googling to see what the better (free) options are these days.