5e ogl sheet, Changing the Ability Score required for a spell saving throw.

Hello! I have a new spell I'm attempting to add to the 5e ogl sheet. The issue is that the saving throw forced on the target is a choice of the caster's. I understand how to create a query macro '?{Which Save| ability Score, ability score| ab...}. However, I do not know where to put that query into the sheet. When adding a spell manually, there is the SAVING THROW option with the drop down arrow for each of the ability scores. I was hoping to encounter a query option here but alas there is not.  Any help resolving this issue would be much appreciated! And thank you for your time. 

My guess is that reason there is no variable Saving Throw option is because, as far as I know, there is no official spell that does that.  My suggestion is to put the query directly in the spellcard, don't use an Attack for the spell unless the spell requires rolling an attack roll.  Example: When hit by this spell the target must make a DC [[@{spell_save_dc}]] ?{Select Save?|Strength|Dexterity|Constitution|Intelligence|Wisdom|Charisma} saving throw.  If it does require an attack you can put that in the Description of the attack.

I appreciate the response! I could have sworn there was a wizard subclass feature that did this for certain spells, but it could be homebrew I'm thinking of.  Your suggestion is the method I'm currently employing. However, I was mostly curious if there was a way, in the sheet, to add in a query option for spell saving throws. This does not seem likely, as I looked up and down the attributes/abilities tab to no avail. 

No way in the sheet that I am aware of.