I think your not giving some basic mechanics enough credit here. Yes, many people certainly only vote for the main parties because they feel that their vote may be “wasted” on a minor party. However this poses the question “How did the main parties become the main parties anyway?” When considering how to succeed as a minor party that question should inevitably be something that one must answer.
If you look at the behavior and voting patterns of people they are actually quite unconcerned about empirical data. Instead they are concerned with “virtue”. Is the candidate “virtuous” in their eyes? Does the party express and support virtues that they hold dear? Big parties campaign on virtues that are broad range and therefore gather a great deal of support. You mentioned gun control opponents in the United States and that is an excellent example of this. These people may actually vary quite a great deal on other “virtue” issues such as homosexual marriage, however they all personally believe that their legal rights are fundamentally secured by an armed and capable populous. Therefore anyone who campaigns on the perceived virtue of “guns are moral, because they defend people and secure our rights” has a large number of potential supporters.
Therefore if one is trying to get a smaller party of the ground the key is instead to take ownership of a series of virtues and run a persuasive campaign to help the public not only accept but believe in these virtues. In other words, the party must relate with the public and the public must relate with it. There are of course mitigating circumstance. The person who controls a “higher virtue” that is as equally accepted as someone who controls a “lower virtue” will win out. This is actually why again opposing gun control in the United States is actually an effective political stratagem. Because people believe their rights are secured by those arms that means all those rights, other virtues are subservient to the ability to own modern effective weapons.
So supposing my objective is to successfully express the pro-transhumanism cause in the government. We have already discussed “Is it possible to start a new party along these lines?” We have recognized because transhumanism even accepted by the populous is a “lesser virtue” therefore if it the central virtue of said new party the new party will remain a minor actor on the political scene. When viewing the political situation without bias as a pragmatic man the question then arises “can I subvert a major party to my ends?”
We recognize that the major parties have the strength we need. Therefore we need to figure out what sort of pressure and incentives we need to encourage the main party to behave the way we desire. In these calculations we of course must ensure we pick a major player whose primary virtues do not come in conflict with our desired virtue. Of course this still asks how can this be done? The first obvious step of course is to target the voting population that said party depends upon and instill the desired virtue in them.
That of course creates a whole new set of problems! How DOES one change a group of people’s moral compass? Even a minor change can be hard.