force github file extension for fetch? (tar.bz2 instead of tar.gz)

[Gary Aitken]

In attempting to build a new port (prusa3d slicer) I need another new
port (wxWidgets).  The original distfile fetch of wxWidgets was a .tar.gz.
The configure phase had an error; a search for the source of the error
turned up a bug (old) which claimed the error was solved by fetching the
distfile as a .tar.bz2.
.tar.bz2 is the github *nix distfile for the port.

Is it possible to force fetching of .tar.bz2 instead of .tar.gz if both are
available?  Or how does one get around the problem?

11.2-RELEASE-p4
relevant Makefile details:

PORTNAME=       wxwidgets
DISTVERSIONPREFIX=      v
DISTVERSION=    3.1.2
USE_GITHUB=     yes
GH_ACCOUNT=     wxWidgets
GH_PROJECT=     wxWidgets

Thanks,

Gary