I put my level dimensions on the detail view, which means that it appears on the layout after drag&dropping it - like you would with "normal" dimensions.
In the Dimension tool you have the option to change to level dimensions.
You can put custom text into the measurement field, so you can have the same output as you would on your elevation/section level lines.
If you are having problem displaying the correct value, I know a lot of people who tend to move their details all around into one place... In that case some workaround is needed: place a hotspot relatively to your detail, change the user origin to that point and set the option to measure from there in the detail tool.