Buying land and building a second dwelling... what is the best way?

[Drex Tanner]

So I am looking for creative ideas others have done for the following situation: 

My father owns his home on a 1.5 acre lot. About .6 acre of it is just pasture behind it, that was used for hobby cattle. I am wanting to build a home on that land, but the city will not let us subdivide the land (parcel not big enough). 

I am looking for any ideas from the community to the following 2 questions:

1) Is there a way to petition the city to allow the subdivide of the parcel? (Gilbert AZ) (from my research, this seems unlikely). 

2) What would be the best/most creative way to finance it, if unable to subdivide does not work? 
(My idea so far: My father cash out refinances the property (he has plenty of equity) - he puts my name on the refinance, and use the cash to build the second house, and I would pay the difference compared to his current mortgage). Is there a better way? 

Would love any creative ideas to the above questions, thank you!

For context: 

- we have a great relationship, and they are a few years away from retirement

- I would not be able to afford to buy him out all the way of the home with a traditional loan, and they do not want to move anytime soon.

[Mike Wood]

@Drex Tanner  You can read up on the local zoning regulations, this will tell you what you what your able to do.  Determine what you can not meet.  While generally not required, the more information on what your going to do, like building plans, will help the variance board to understand the need (and even allow them to limit the variance approval to a specific set of building plans).  Also, if you can find any other properties that match or are close to what you want to do that would be helpful as it shows precedence.

I find my local staff do not like to approve blanket requests, but will more seriously consider things if you shown the exactly what you are planning on doing.  I guess it keeps the scope of the approval limited and avoids others from trying to use your approval as justification for future approvals.