Two exercises you could try in the initial stages are:
1-Let the patient lie on the affected side, ensure that the weight is not borne at the shoulder, but over scapula. For this the shoulder is abducted and in Ext. Rot'ed position, with elbow in flexion. The affected LL is in flexion at knee. Now abduct the unaffected LL & UL at same time.
2-While working on the trunk, even before you have started with standing, ask the patient to flex the unaffected LL & UL at the same time.
These two exercises can be used prophylactically. Most (L) Hemi's are pushers. During ambulation, You could ask a relative to stay close to the patients unaffected side.
asha