It seems you can use relative URLs for submodules. From git help submodules
:
COMMANDS
add
[…]
<repository>
is the URL of the new submodule’s origin repository. This may be either an absolute URL, or (if it begins with ./ or ../), the location relative to the superproject’s origin repository
So, if you follow the same naming convention in both sites (ie, github.com/you/parent-project
, bitbucket.org/you/parent-project
, github.com/you/child-project
and bitbucket.org/you/child-project
), you should be able to set the submodule like this:
[submodule "programs/mgr-nancy-demo"]
path = programs/mgr-nancy-demo
url = ../mgr-nancy-demo.git
Test it – YMMV!