There is currently no way to achieve it by using standard instruments of API Blueprint.
Neither
+ Values
+ `A - means something`
+ `B`
+ `C`
or
+ Values
+ `A` means something
+ `B`
+ `C`
will work correctly. I filed a feature request under API Blueprint's repository. If you want to be part of the design process and help us to get the best solution to your problem, you can track it and comment under it.
Appearance
I understand that rendering of this feature isn't very nice in standard docs.

However, in "beta new docs", it looks much better. Try it out - in settings, turn on following switch:

Then the rendering should look like this (two states):


Using tables
When in troubles with API Blueprint, you can always use plain old Markdown in endpoint's description to supplement or substitute what's missing. E.g. you can freely use tables as an addition or replacement to the Values
section:
# My API
## Sample [/endpoint{?id}]
Description.
| Value | Meaning |
| ------------ |:----------------:|
| A | Alaska |
| B | Bali |
| C | Czech Republic |
+ Parameters
+ id (string)
Description...
| Value | Meaning |
| ------------ |:----------------:|
| A | Alaska |
| B | Bali |
| C | Czech Republic |
Description...
+ Values
+ `A`
+ `B`
+ `C`
Rendering of tables in old and new docs:

