Unless I've misunderstood, you could use standard fields to accomplish this -
- Create an MText object
- Right click within the content > Insert Field
- Create a field referencing your first drawing property
- Right click again within the content > Insert Field
- Select Formula field
- Right click within the formula pane > Insert Field
- Select your numerical custom drawing property
- Type +1 after the field, and then insert it
Well I'll be damned. Didn't realize you could nest fields like that and reference other properties.
That's awesome, thanks Lee!