A few suggestions:
If it is uncrossed or crossed with two lines and nothing written between them, you should be in a position to have him endorse it and lodge it to your account.
You could try lodging it using one of the automated lodgement machines in your branch.
You could as Brendan suggested put it in an envelope with a paper lodgement slip and put in the the lodgement box or postbox in the branch. Many branches no longer leave lodgement slips out, you might have to ask for one at the counter.
If its for a smallish amount, you could use it to part pay a utility bill using the GIRO slip
Or as a last resort, he could contact the payer and ask them to cancel it and pay by bank transfer, giving your IBAN.