I’m not sure that is possible anymore. We booked a trip online a couple of weeks ago and online, EBCI was offered to the entire party but no choice for each individual traveler. So I called Southwest to ask about this apparent change to the online reservation system. The Southwest agent informed me that now all of the people with the same confirmation number, basically everyone on the same reservation, either have to purchase EBCI or none of them can.
I asked if he could tell me why the change in policy - he claimed not to know, but guessed it was to help with the issue of seat saving.Travelers only paying for one early bird check in an attempt to get a lower boarding position then trying to “save” seats for other passengers they might be traveling with who failed to purchase EBCI.