When centering a single letter, the work is quite easy.
A construction Line, four points, and three vertical horizontal constraints need to be added to each letter. And yes that's a bit of a pain.
Steps:
1 - Create a center anchor point for the letter
2. - Create the letter slightly above and slightly to the right of its center anchor point.
add a construction line from the lower left corner up the side even with the top of the letter or number.
3. - Add three points
- add a point to the midpoint of the construction line you just created. It will be below the midpoint of the longer construction line that makes up the bounding box for the text.
- add a point to the center of the bottom construction line
- add a point to the center of the top construction line
4. Add horizontal and vertical constraints
- add a horizontal/vertical constraint between the top and bottom points that you added
- add a horizontal/vertical constraint between the point where you want the letter to the point on the side of the bounding box
- add a horizontal/vertical constraint to the point on bottom of the bounding box
A bit of extra work due to the lack of a center point for the letter and a bounding box for the font that is not the same shape as the font.