What do you do if you really want to give your estate to someone?
One must transfer the estate while he is still alive by making a Kinyan. (This can be accomplished even without the presence of the beneficiary through Zechiyah.) The giver must specify that he is giving the estate "me'Achshav u'Le'achar Misah" (so that he can continue using it until he dies.)
Another method commonly used in Halachic wills is that the distributer of the estate "forces" his heirs to comply with his wishes by obligating himself to pay great sums of money to specified people on the condition that the heirs do not agree to distribute his estate as he specified. This neatly avoids any problems of "Davar she'Lo Ba l'Olam."
See attached file for an example of such a document (courtesy of my brother, Rabbi Elimelech Kornfeld of Ramat Beit Shemesh).
K'vod Harav Kornfeld, The last one sounds like a chatzi shtar zachar to me. I have one. The way I understood it is that I obligate myself to a huge amount of money to a Yeshiva or person, more money than I'll ever have. If my children contest my secular legal will then the obligation takes effect. If they don't it doesn't.
I'm still not 100 per cent sure why that means I'm not oveir on the Torah's intent on nachlos.
Both of the Shtaros I sent work the same way; one is to obligate heirs to follow *his* will, the other is for the husband to obligate heirs to follow his *wife's* will. They both work by self-obligation, as you wrote. In essence, this is the same as the first way we mentioned to grant an estate -- by making a Kinyan during the life of the giver to grant large sums of money to other people. The point that is added in these Shtaros is that the giver just uses this obligation as a way of "forcing" his heirs to do whatever he wants with his money. In this way, the giver does not have to worry about the problems of Davar she'Lo Ba l'Olam etc.
When one gives gifts to others during his life it is not called "overriding the Torah's laws" of Yerushah, since those laws only apply to what *remains* after death. If a person dies penniless, he has not "thwarted the Torah's will."
As for the tactic of forcing the heirs to give to specific people in this manner, this too does not thwart the laws of Yerushah since the true heirs inherit exactly what they are supposed to; it is *they* who "choose" to give the money to whomever they want (at their father's prompting).