I had considered:
Granting a player a temporary building, which gives a free technology
Blocking research of tech, which are not spell research, while the player has that building
Removing the building, whenever a spell research tech is acquired.
Seemed like a plan but when a building grants a tech, the player is steered to the Technology screen and can't get to the spell research screen to make a choice.
Does anyone have a suggestion of an efficient way to give a player a free choice in spell research?