IAS 40

Could you please help me explain this question in BPP workbook:

Burdock has a financial year end of 30 may 2006. It owns a number of prestigious apartments which it leases to famous persons who are under a contract of employment to promote Burdock’s fashion clothing.
The apartments are let below the market rate. The lease terms are short and are normally for 6 months. The leases terminate when the contracts for promoting the clothing terminate. Burdock wishes to account for the apartments as investment properties with the difference between the market rate and actual rental charged to be recognised as an employee benefit expense.

The problem i have is that i do understand that since the property is let below the market rate and let to employees, it cannot be recognised under IAS 40. But what about the employee benefits? why can’t we recognise the difference as per IAS 19?