hi
you can use support for the client to stand with
ask him/her to stand on on leg with hands on the back of he chair......and when he feels the body is about to sway and his legs are giving way he should take all the weight of the body on hands rather and rest....
but DO NOT SIT.......let him balance a bit and then again stand by taking weight on legs.... with time he will be able to stand for longer with whole weight on legs.
[also check for neurological disturbance for imbalance IF muscles are not affected]
hope its usefull