Effective August 1, 2012, a new wrinkle is added to the IID exemption for vehicles that are used by the IID restricted driver and - owned, leased, rented or in the temporary control of the employer.
"However, when the employer's vehicle is assigned exclusively to the restricted driver and used solely for commuting to and from employment, the employer exemption does not apply." (my emphasis) RCW 46.20.385. SHB 2443.
This change to the law appears to preclude the exemption if commuting only. Although, it would appear to create many many grey areas and leave some room for interpretation.