Benefit Cap and UC - no personal allowance left?

Client is on UC and is affected by the benefit cap. He is a single person living in London. 

He is in temporary accommodation but LA has discharge duty which means that for benefit purposes he is not in temporary accommodation. 

I am aware that the benefit cap is applied to the whole award and not separate ‘elements’ of the UC claim but this is leaving him with very little or no personal allowance at all. 

Is there any way around this? He is in receipt of DHP to top up his rent but DHP obviously does not top up his personal allowance