Assuming your first and last name are separated by a space, you can use the Substitute ( ) function, like this:
Substitute ( name ; " " ; ", " )
Use a Set Variable script step to set a variable equal to that value and put the variable on your layout. (You could also use a global field and a merge field.)
If you names are in the list, you would just need to slightly modify Mike_Mitchell suggested Substitute:
Substitute ( ("John Smith¶John Doe¶Wendy Smith") ; "¶" ; "," ) will result on
"John Smith,John Doe,Wendy Smith"
To get the names into the list, just use list on your relationship ->