If it is temporary, then you are considered to be away from home and all of the expenses are deductible. If it is indefinite (a subjective term dealt with in the courts, but the IRS pushes for the one-year rule), then you cannot deduct them.

Since most senior missionaries are out for longer than a year and they typically know that to be the case going into it, they fall under the indefinite periods and those items are not deductible when paid directly.