But I'm still curios what the canonical approach may be

The win32/makefile.mk (written for dmake) in the perl source contains:

#
# set this to point to cmd.exe (only needed if you use some
# alternate shell that doesn't grok cmd.exe style commands)
#
#SHELL        *= g:\winnt\system32\cmd.exe
[download]

I guess therefore that, in your makefile, you might want something like:

SHELL        *= C:\path\to\your_shell.exe
[download]

Cheers,
Rob