I don't know if this is valid or applies to your specific situation, however, considering the substantial differences in healthcare services and the (sky-high) cost in the US you may want to look into it. 

I'm looking into the possibility/cost of adding an additional natural gas meter into my duplex.

I am not for breaking any laws, but maybe, there are loopholes where you can have a valid and legal reason to rent the house a few weeks, or a month after you purchase it.I have an employee who purchase a house FHA with 3 percent and he lived in it for only about 3 days.

The 3 day notice must be properly written and properly served in order to be valid.

@Jay Hinrichs That's a valid point.

@Ryan Webster I have done plenty of multifamily ground up as well as adaptive reuse and mixed use.Your concern regarding supply is valid.

All gas furnaces are newer, but I don't know specifics about any of the other mechanicals.  

For the building as-is, the taxes are $6,600 per year (pulled from http://tax1.co.monmouth.nj.us), water / sewer is included at ~$2,500 per year, gas and electric are separate, property insurance is at $6,500 a year and repairs are at $75 per unit per month.

I would outline all that you have done to this point - including the lack of gas reimbursement- the work you have done while accommodating the pretense of his property but the time has come to for you to have the full use and enjoyment of your home. 

@Pope Lake I have all of my tenants pay for gas and electric.