Scroll to end of textbox even when not in foreground

I'm trying to get a textbox to scroll to the end. I'm using the usual code for autoscrolling, but this only works when the application is in the foreground, which is an issue for my particular use.

textbox.SelectionStart = textbox.TextLength;
textbox.ScrollToCaret();

Is there a way to adapt this so the box will continue scrolling even if the application is not focused?

Edit: I should also mention that I am using appendText, and is not autoscrolling automatically like it should be.