For legal opinions specific to your particular situation please contact an attorney well versed in real estate and mortgage law.
The Federal law known as Preemption of Due-on-sale Prohibitions 12 USC § 1701j–3 states:
“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 a residential manufactured home, a lender may not exercise its option pursuant to a due-on-sale clause upon—…the creation of a lien or other encumbrance subordinate to the lender’s security instrument which does not relate to a transfer of rights of occupancy in the property;….”
An attorney may be able to draft the wording of the easement to explicitly state that the easement is subordinate to the lender’s security instrument. This is another good example of why these type of questions should be directed to competent counsel. Real estate law is not a DIY project.