Intellectually impaired cardio pt

Setting: RPH Oncology ward
Patient: 38yo male with a congenital intellectual impairment (not classified)
admitted with pnemonia (3/52 Hx)
on a b/o progressive lung cancer with bony mets

The pt could not speak so the subjective was taken form his supervisor of the hostle he lives at. The pt was prev amb with a W/S and was independent will all ADL's.
The pt can understand language just not verbalise it.
Pt could maintain sats on RA, had widespread insp crackles LZ, R MZ
It was hard to gain the trust of the pt and he would not cough or breathe deeply on command. He would cont to take off a neb if applied (face mask).
Often he would hide under his covers and he would not cont to sit upright if put in sitting would slouch down in bed and tuck chin.
Much time was needed to gain trust before treating him. This was very detrimental to the length of treatment for other priority pt's.

The rationalised best treatment for his chest would be to amb. He had standby STS and good static standing balance, tests of dynamic where limited due to poor attention and compliance!
Upon amb with a WZF 1 standby assist the pt looked steady and had a good gait pattern.
Then due to his intellectual impairment? the pt took his toes off the floor, crouched and tired to sit on the floor.
I had to assist a decent to the floor so the pt did not fall...
I felt the only option for the pt to amb safely was with 2 mod assist. yet the effect of increasing tidal volume and mobilising secretions was minimal.
I reverted to simple STS and bed mobility ex to mobilise secretions which were effective (sm amounts of P3 sputum) but not enough to clear the majority of secretions. The pt also hated doing this.
I let the staff know about all this and enco the N/S to still try nebs and sit up.

I felt very sad for the pt and his family and carers, also a little hopeless in this situation.
Could you suggest other Rx strategies?