That seems like an over-simplified or even naive example. Like, a candidate moving their platform has just as much chance to lose 5% of their base as it does picking up those third party votes.
Also, realistically, there isn't one singular thing that people vote third party for - there's lots of little "one things" that particular individuals vote third party over, so it's a more difficult matter than simply "moving closer to those party's positions" - it's going out and figuring out what exact positions those votes left you for and trying to incorporate them piecemeal into your platform, all in a way that maintains your current base, or at least gains you more votes than you lose...
IDK man, I don't see the draw there. Surely it's much easier to find that 5% in centrists or undecided voters, rather than the very principled people that decide to vote third party.