Adding a mate??

I have a 12 gal. nanocube that currently has a two year-old true perc (about 1-1/2") who is the original  inhabitant of the tank.  I also have a pajama cardinal (about 1") and a firefish (about 1-1/2").  I also have a small sarcophyton that the perc. has taken a liking to and is beginning to host in.  The perc is definitely in charge of the tank and tends to bully the other two fish a bit.  Lately I have been lamenting that it would be nice to have a mated pair of clownfish in this tank so I have been considering adding another clown.  Here are my questions:

A.  Is this a good idea to add another fish to this sized tank (currently, I do weekly 10% water changes, but could easily up it to 20% if necessary to account for the additional load of one more fish)?

B.  With the existing perc already dominating the tank is it wise to add another clown to the mix? Do you think the new perc would get the brunt of the bullying being the new kid on the block?  Would it temper the existing clown to have a mate? 

Looking for any input or experiences you may have.
Thanks!

As far as fish load goes for your tank I belive that your really close to it.  But that is just me as for another clown.  I say you could if its smaller and unsexed or if you know for 100% that its a male.  If its not sexed it will get pushed around but I belive that it will take it for a mate.  Im not the best person to ask on this Im sure others will tell you something that is better than I can. 

Corey,

I was thinking about getting a small one just for that reason.  I've read Wilkerson's book back when my clowns at home were laying eggs.  It's such a great book!  I'll have to go back and read that section again on pairing.