Man I got a blinder for ya.
Done this loads of times and it works a treat...
All ya need is a bottle Talcum Powder or Icing Sugar and a record sleeve from an old 33.
Fill the record sleeve with the very fine powder and carefully feed the open end under the closed bedroom door of the victim. Now jump on the record sleeve!
The effect is fantastic...the inside of the sealed room is covered in the very fine white powder but obviously there are no foot-prints leading to the door and they will have no idea how you did it...
Couple of pointers...
Make sure you clean the area outside of the room if you spill any...the mystery of how it was done will drive him /her crazy!
Watch it when you jump on the sleeve...it can be very slippery on carpet!
For extra fun wait until he/she is drunk and then do it with them in bed...they will have no idea what has happened during the night! (Make sure you use Icing Sugar if you are doing it with the in bed, talc can be harmful if inhaled in large quantities!
I have got hundreds of these kind of things if you are interested...I am a master practical joker and have been doing it years!!!