You can use a virtual screen that is larger than the real screen resolution and draw on that -
// Set physical screen resolution
SETSCREEN 640, 480, 0
// Create a virtual screen that is larger than the physical screen
// Do all actions on the virtual screen
// Draw lots of random rectangles on the virtual screen
FOR n=0 TO 1000
// Grab a portion of the virtual screen
// Use the normal, visible screen
// Main loop
// Repeat until ESC pressed
// Show portion
// Refresh everything
// Repeat the main loop unless condition is broken (ESC pressed)
The example above draws on the virtual screen and grabs a portion of it that is beyond the 640x480 limit of the actual screen, then displays it in the main loop.
Or do exactly what Mr taToad suggest and use LOADANIM.