My Poser is on my laptop as well, my runtimes are on an external drive and every now and then when I know that work is going to be boring and I'll be sitting the majority of the day doing nothing, I'll transfer a few runtimes to the laptop and take them with me.  When I get home I just delete them off the laptop and plug back into the external.

When I set my desktop back up, I'll probably just keep using the external drive even though my desktop has a 500 gig hard drive in it.  hahaha

Go for it, it's a sweet set up and your laptop will be happy that it doesn't have to scan your runtime all the time.