Excerpt from Rationalist Judaism:
In his discussion of this topic, both in a shiur transcribed online and in Responsa Minchas Asher II:58, he acknowledges the problem with the notion that you can do mitzvos and credit the reward to other people. Rav Weiss notes that Maharam Alashkar and others state clearly that the reward for mitzvos cannot be transferred to other people, and that they give powerful reasons why. However, he takes the approach that it simply cannot be so. Why? Because everyone does it!
That is actually his position, and he says it explicitly in his responsum. If everyone does it, it can’t be that it doesn’t make sense! He tries to come up with a way of making it work even according to Maharam Alashkar et al., but is forced to admit that there is no convincing way to do so. And he tries to find earlier sources who defend it, but they are extremely limited (as they are referring specifically to charity) and tentative. Accordingly, Rav Weiss concludes that it simply does work, albeit inexplicably, and that it is one of the secrets of Divine providence.
It’s simply astonishing. It means that Rav Weiss is saying that all the Geonim and Rishonim and Acharonim who said that it doesn’t work, are wrong. But he would rather do this than say that the conventional practice today is baseless. There are many cases where we defend historical tradition, even on weak grounds, shelo lehotzi la’az al ha-rishonim (so as not to cast aspersions on the earlier generations), but this is the opposite; discarding the historical tradition, shelo lehotzi la’az on what people do today.
I didn’t check within, but I have seen many similar things, myself.