In fact, we Mahayana Buddhist should "give away" and dedicate --ALL-- the merit of our good Karmic acts to others, and thus, for example, every Zen ceremony has an "Eko" (Dedication) recitation dedicating the merit of that ceremony or practice to others. You do not need to "do" anything really in order to achieve that, except to wish so in one's heart. The words of the "Eko" simply express that wish.
A "win win win" reverse triple "pay-off" of doing so, by the way, is that the "donor" traditionally thus gets a "double-triple reward" ... both the effects of the "good Karma" acts which are donated, but yet are somehow also kept too PLUS EXTRA "good karmic points" for the good act of donating!!

That's on top of the donee benefitting too! All these "karmic points" are traditionally said to eventually manifest in good effects, either in this life or in a future life (in this case, both for donor and donee).
For someone like me who is less a "literalist" on all this Karmic accounting, I still believe that our good acts in life generally tend to have good effects, both for ourselves and others who are touched by our acts (sadly, our bad acts all tend to hurt others and us too.) "Dedicating" to others is still a good thing, even if not literally so, because it keeps us thinking of others, trying to help others, and less selfish for ourself.
Here, let me dedicated this:
"May the merit of having written the above benefit all sentient beings everywhere."

Gassho, J
stlah
PS -
By talking to your spirit guide?? - I bet old Shokai just meant that he is not such a literalist on these things either.