When I dive under the ice I make sure to have a environmentally sealed regulator and that it is properly adjusted for the diving that will be undertaken. Redundancy is a critical component of planning for these dives. There are many techniques to achieve this, personally I dive a Drysuit for redudant bouyancy and doubles for redundant air, in addition to my buddy.
Does the crystal clear water and extreme focus required to get this done safely sound appealing? Drop us a line and we can help you on your way!