Yes. You don't multibox by "driving" both characters at once (with a very few specific exceptions and for very short periods of time). You follow your main by using /follow macros.

For Rift (assuming your main char is named Beelzebubble):

/targetexact beelzebubble
/follow
/targetlasttarget

There are tweaks to that macro based on how you use targeting and focus but that's the basic idea.

[edit] Note that you will want to prevent normal movement keys from getting to your alt until/unless he is your actively-controlled character. I'll let others describe that in terms of ISBoxer setup.