That makes a lot sense! I'm not familiar with that process (as a gardening technique), but I have heard about it. I have heard it's a lot trial and error. Not sure I have that kind of patience, but good for those who do
The simplest example, because of the size of the flowers, is courgettes/zucchini.
When you have a male flower of one variety open, and a female flower of the other variety almost ready to open, you take the male flower, strip off the petals to leave the stalk and the pollen infested stamen, then gently open the female of the other variety enough to put the male inside and rub it gently against the stigmata.
Withdraw the male flower, and tie up the female with a soft yarn, like wool, so that it is impenetrable for other pollination.
Let the courgette fully ripen (probably to a marrow) and the plants grown from its seeds will be a hybrid.