I would like to see a specific commit in Beyond Compare or any other separate diff tool while viewing it via git show
. I tried looking at help of git show/difftool/
I think that git show is based on the tool set in the GIT_PAGER variable. I don't use Beyond Compare but i think that you can try something like this:
$ GIT_PAGER='bc3' git show
Maybe you should fill the GIT_PAGER variable with some additional parameter that allows bc3 process the input.
There are more suitable ways to persist the pager. This question can give you more tips about how to do it.