If the minister has no access to a sacristy, what should be done with a host that has been spit out?

My understanding is that hosts that have been spit out by a communicant who is unable to swallow must be dissolved in water and then the water is poured down a sacrarium. But what do you do if you are visiting a nursing home or a homebound communicant where it is impractical to get to the sacristy? The GIRM is vague on these special circumstances.<br />