Note: The following does not answer the question.
If the order of the addends is considered, there is a simple approach.
Place the 8 objects in a row, leaving a space between them.
. . There are: spaces.
Select 2 of the 7 spaces and insert "dividers".
. . There are: dividers.
This diagram represents:
If the order is considered, the number of ways is:
Can we eliminate the duplication included in this method?
I don't know . . . I've tried and failed.