There's no good way to achieve this I'm afraid, this is mainly because Word only allows one style of citation in a document in order to keep a consistent look throughout the whole document. Therefore there really is no other choice but to choose between either your casual style or the APA style.
The closest you could get to "bending" the citation to look as you want without changing style can be achieved by adding each source as a separate citation instead of adding two sources to one citation, writing out the separating text as plain text and finally right clicking on each citation and choosing Edit Citation and click Suppress Year. The result should look something like
Indeed, further work by authors such as (Kim) and (Cagnon) has shown.... Not perfect but it might do for you.
If you could settle for casual style of citation throughout your whole document then you could achieve this by creating your own bibliography style. Word stores these styles in XML form to the directory Word was installed to. If you are looking at doing this sort of thing then I highly suggest looking at BibWord which is a tool that helps make it easier to create new bibliography styles. They also have plenty of existing custom styles that can be used.