I do a therapy called Tibetan Acupressure Head Massage which is performed with client lying down the whole time, either on a treatment table or reclining chair. In Tibet it would have been done with the the reciever's head lying in the lap of the giver.
I personally think it is much more relaxing to recieve than IHM, and also more comfortable to give as you sit down.
The techniques are different than IHM. There is a lot more face massage and a lot less shoulder/upper back, but the therapy is very adaptable and it is easy enough to do the upper back with the client seated before lying them down for the 'main' treatment. It also combines well with other therapies, expecially Reiki, Aromatherapy, beauty treatments like facials etc.
The Tibetan Acupressure points can also be incorporated into IHM routines. Also makes a great short treatment for events and pamper parties.