Not easily, but it can be done. :-) Here's an example.
I use the WikiDroyd application  so that I always have an off-line version of the WikiPedia to hand. I'd much rather not use up my valuable internal storage for this, though - it's over 6GB of data, and I have 32GB of space on my external SD. WikiDroyd keeps its data under /mnt/sdcard/WikiDroyd, and that's pretty much hard coded AFAICT. What I need to do is to make WikiDroyd *think* it's looking at /mnt/sdcard/WikiDroyd, whereas actually it's looking at /mnt/extsd/WikiDroyd. And because Android is actually running Linux under the covers, I can do exactly that.
Firstly, I use some file manager or other  to create both /mnt/sdcard/WikiDroyd and /mnt/extsd/WikiDroyd directories. I put the data files I need into /mnt/extsd/WikiDroyd. (Any files that WikiDroyd downloads will end up there too.)
The I create a shell script somewhere. This is just a text file, created and edited with a plain text editor such as Jota . The name of the file doesn't matter too much; I've called mine mound-extsd.sh so I know what I'm looking at if I stumble on the file later. The file contains the following:
# Wait for external SD to be visible
while [ ! -e /mnt/extsd/WikiDroyd ]
echo Not found
# Mount external directory under internal
mount -o bind /mnt/extsd/WikiDroyd /mnt/sdcard/WikiDroyd
Lastly I need to arrange to have this script run when I boot my phone. Tasker  can do this - tasker can do just about anything - but you can also use something like Script Manager . You'll need to run the script as root.
That's it. Now when I launch WikiDroyd, it can see the data files I have on my external SD card.
Note that if you can configure an app's file location, that's a better approach than fiddling around with filesystems like this. But if you are dealing with an app that doesn;t mhave that option, this might be useful.
Also note that mounting the external SD card takes some time. Any apps that might start running before the mount has taken place might not be able to use this approach. Evernote is an example of this.
 I recommend Total Commander: https://play.google.com/store/apps/detail