1031 Exchange + Personal Residence Exemption in One Duplex

[Joe Coyne]

Here's one for the community:

I currently occupy one unit of my duplex, while renting out the other.  I'm considering selling the duplex while it's still 50% personal residence.  I'm looking at a total gain on the property of about $72,000.  I've separately calculated (per IRS guidelines) the gain.  

As I'm a CPA, I'm not going to mess around with fudging the numbers, although it would be quite easy to do so with the improvements.  Anyways, as you can see - the majority of the gain is on the rental property.  The IRS says you need to divide the sales price evenly (if you calculate depreciation on the rental based on an even initial basis, which I do), although I could argue the value of the personal residence is double that of the rental - hence all the improvements made.  Could I alter the proceeds proportions?  Also, since I'm using the personal residence exclusion on the personal portion of the duplex, am I prohibited from using a 1031 exchange on the rental portion?  

Any comments or questions are appreciated.  Thank you.