Is it possible to make guacamole without acid?
At its simplest, guacamole is just mashed avocado. Avocado is not particularly acidic on its own, so add whatever non-acidic ingredients you like. 

Consider cilantro, sour cream or whatever low or non-acid flavorings suit you.

See: Browning Avocados - What Helps? for more on acid and avocados.