I've heard of it happening, but not in today's economic climate. Yes, technically, it could happen. I'm not a lawyer, so this is not legal advice, but the sale or transfer of any portion of your equitable interest in the property is sufficient for a lender to invoke a due on sale clause.
One way you might protect yourself is to create an Illinois-style land trust. You then transfer your property into your land trust. That will not trigger the due on sale clause; the Garn St. Germain specifically exempts this:
(d) Exemption of specified transfers or dispositions
With respect to a real property loan secured by a lien on residential real property containing less than five dwelling units, including a lien on the stock allocated to a dwelling unit in a cooperative housing corporation, or on a residential manufactured home, a lender may not exercise its option pursuant to a due-on-sale clause uponâ€” .....
(8) a transfer into an inter vivos trust in which the borrower is and remains a beneficiary and which does not relate to a transfer of rights of occupancy in the property....
Once you transfer your property into an inter vivos trust in which you are and remain a beneficiary, then later, separately, you may add a resident beneficiary to the trust--resident because they will reside in the property, and beneficiary because they will be one of the beneficiaries of the trust. They'll execute a possessory agreement with the trust--somewhat similar to a lease--but remember: they, just as you, own a portion of the trust which, in turn, owns the property. They will pay a monthly fee to the trustee, who will use the funds to pay the mortgage, condo fees, and other expenses. At some point in the future (presumably after the value of the condo has risen so that it's worth more than is owed on it), the condo will be brought out of the trust and the resident beneficiary will have the right to purchase the condo at full fair market value. At that point, the condo is refinanced; the title is placed in the new buyer's name, and you're off the financial hook.
For more information on how the whole process works, go to http://www.landtrust.net
Hope that helps.