I agree with everyone a thank you for coming and enjoy your night should be said by the bride, groom, or a parent. You can ask the dj or reception facility to handle who gets up, or who is being served first. They usually handle this after the prayer so I don’t' know why it would be any different for no prayer.... Writing the mini speech should be no big deal. Try starting with: We wanted to thank everyone for sharing in our special day. Then add something personal and end with: Please enjoy your evening, eat, dance, and be merry.