Group showing just 1 e.g. user without do a search for users


this might be a dumb question:

so i have a particular user i want to show in a group: how can I display this user (i know his unique id) without running a do a search for all users? (it is not the current user)

what about if it is 4 users but in a repeating group?

can i just paste 4 unique IDs somehow??