i've done a beat in realtime before. i do it a lot.
this is what i do. since i record into cool edit pro i hit record in c.e.p. when i start off of course the beat may need an intro. so before i press play i have all the tracks muted that i dont want playing. i press play and start recording the beat. gradually i unmute the tracks in the order i want them to come on. for example...when it startes playing i may wanna bring the hihats in so i spin the wheel to hats and turn it on when i want it....then spin the wheel to the kick then snare and turn those on etc......when the verses come in i spin to the instrument i wanna turn off and mute that track. then bring it back in when i want it in. i guess this is what you mean by "real-time."
but i do it all the time. its not hard
but feather boy is right bout the sequencing. .. .