Dude, I wouldn't worry about space. Even in Emerald, there's a ton of space for new songs.
Anyways, what you want to do is at the end of a song, place a 0xB2 byte, followed by your offset, then end it with a 0xB1. If you want to jump to another part of a song (like if you have an intro to a song, like a battle theme), use a 0xB3 byte followed by your offset. I'm not sure if you need the 0xB1 but put it in there to be safe. BTW, 0xB1 is the stop command.