I agree with the above users. Doing this would be a logistical nightmare and would bring up more problems than it would solve. I won't bother adding to the list of hypotheticals, but I instead want to make it clear that what you want is still entirely possible through simply attending one uni.
For instance, you could do a Bachelor of Arts, studying whichever politics/international relations subjects you want to. Simultaneously, you could use your free electives to do one programming or computing subject a semester. It would be possible through the Melbourne model to finish your BA with the pre-reqs for a Master in Information Technology solely by doing computing subjects in your breadth slot. If Melbourne isn't your cup of tea, basically every uni has slots for electives which don't have to be in your faculty--especially for the areas that you want.
Failing that, you could technically do a double degree in Bachelor of Arts/Science (Monash comes to mind, but there may be other unis if you check it out). I feel like you're trapping yourself inside the idea of going to two unis, when it's not necessary at all. It may seem insignificant now, but the challenge of studying one degree can already be messy enough with all the admin stuff in the background (e.g. how do you receive 2 offers from VTAC and accept both, then enrol in both?). Moreover, if you're interested in two entirely different fields with the desire to study both, it seems like you lack direction in terms of what kind of career you actually want to pursue. If I were you, I'd answer these questions before I locked myself into a convoluted plan.
Have a nice day.