Help with feeding

I have a 3 year old who is severely disabled with cerebral palsy he currently drinks from a bottle perfectly I have tried him with beaker but he gets upset as cannot find the spout. His speech therapist has introduced a thickner with a open cup he's getting very frustrated and to stop it from washing him out i feel it would need to be incredibly thick are there any cups or beakers that would allow him to suck like a bottle at his own pace as he tolerates the constituency of a normal drink perfectly thank you