How to install Ubuntu 21.10 to a mapper device (to dual boot LUKS)

Question

I tried to use this very old post as a model to install directly to the LUKS mapper instead of to an LVM set on top of the mapper, but the Ubuntu 21.10 installer explicitly forbids installing to a mapper.

The basic TLDR of the old post was:

1. Boot in try it mode
2. Manually create the LUKS partition
3. Do a luksOpen on the partition
4. Point the installer at the "opened" partition
5. Post install click "continue testing"
6. Back in shell, make a chroot
7. In the chroot setup fstab and grub
8. Close out the chroot and reboot

Of course I'm failing on #4 since the installer wont let me install to a mapper device.

So, is there any way to use the single-partition setup that "Install alongside Windows" uses, but with LUKS enabled? Possibly through scripted installs? This is how I've gotten past some of the more exotic Microsoft prohibitions previously.