In the event that a district boundary line on the zoning map divides a lot of record held in one ownership on the date of passage of this ordinance, each part of the lot so divided shall be used in conformity with the regulations established by this ordinance for the district in which each such parcel is located. If the property owner or such a lot desires, he may extend the use allowed on the greatest portion of said lot beyond the district boundary line in accordance with setbacks and yard requirements for the district into which he is encroaching.