The IRS will not take kindly to you not declaring income. Money you are paid by someone in exchange for shelter is income and is declared on the Schedule E of your tax return. I'm guessing you aren't talking to a real CPA but rather one of the retail tax preparation companies who do not have enough training to truly help you with any semi complicated return. You need a real CPA, not a store-front, seasonal tax office.
There are ways around having turned this into rental property. First of all, you only have to live in it for two of the past 5 years to be able to qualify for the 250k exclusion. And if you are married, it's double ($500k exclusion). If you rent it out for more than 3 years, you can do what is called a 1031 exchange (google this for more info) that essentially says if you sell the property, you have a short window of time where you can invest that money into a new rental and not pay taxes on the gain. Or, you can simply hold onto it for the rest of your life.
BTW, if your AGI is below about $37k if you are single or about $75k if you are married, you won't owe capital gains. Keep in mind though, that if you sell the property for a profit, that amount will count towards your AGI.
If my post and the posts above don't make sense to you, please call a CPA. If that one doesn't make sense, talk to another one. Keep interviewing until you find one that can explain it to you. These are beginner level tax issues for investors, and if you want to be a real estate investor, you need to understand them.