how do you add a single you have bought before the album release of an artist on to the album playlist once you have purchased that

eg

bought the enemy - no time for teras single on release day

then bought the album when it came out

as usual ITUNES say complete the album for X amount as u all ready have one single

but cant add the single to album , i usually make up a play list and copy them to that ,

but must be an offical way ? anyhelp?