In the case of weekly premium policies, there may be a provision that upon proper notice to the insurer, while premiums on the policy are not in default beyond the grace period, of the intention to pay future premiums directly to the insurer at its home office or any office designated by the insurer for that purpose, the insurer will, at the end of each period of a year from the due date of the first premium so paid, for which period the premiums are so paid continuously without default beyond the grace period, refund a stated percentage of the premiums in an amount which fairly represents the savings in collection expense.