Interesting thinking, and I don't want to discourage shooting for the stars, so let's take a look at the possibility.
If Van Hal's heir does not appear to claim the title, then it's technically possible for you to put your name forward as a possible candidate for the other Electors to consider. I think you might just squeak in under the Air Bud rule - there's all sorts of rules restricting wizards from certain political roles and positions of state authority but it's possible nobody actually barred them from being an Elector Count, since it's more feudal than bureaucratic. That said, you can't really consider any of the votes even leaning in your direction as is and there's a number that would be dead against you so it would take some serious legwork.
On the other hand, you could just declare yourself as such and see what happens. You'd have the contacts within Stirland and have impressed the troops enough to make it happen, but you did just lose about half the Army of Stirland which wasn't the most impressive of forces anyway, so your chances of standing against the all but guaranteed military response from the Empire don't look too great. And then there's how the Grey Order would take it: if they'd consider the unlawful seizure of authority 'going rogue' - and, well, they probably would - then your life expectancy would take a nosedive.
If I was approaching this as a player instead of a QM, I'd say this: the only way I could see this going from a longshot to an actual reasonable proposition is if you roped Anton in, rushed a shotgun marriage past your Ranaldite priest friends, and put him forward as a candidate before word got out about his new wife. Magicien grise, éminence grise.