Personally, I wouldn't try to put a spin on an interest in personal finance and attempt to translate that into 3 years of experience in estate or financial planning. I'm sure you're a very qualified writer, but the gamble is that it may come across as sounding like you read a few books and hung out on a forum, so somehow that makes you qualified. Depending on the reader, it could come across as a bad attribute.
What other experience do you have in estate or personal finance, of any kind? Did you take any classes in this area in undergrad or law school? I took wills and estates as well as Accounting for Lawyers in law school, maybe you had something similar? You could emphasize your good grades or passion in this area. Or if you volunteered, or did some pro-bono somewhere for the elderly? Our school offered VITA (Volunteer Income Tax Assistance) where they taught you how to do basic tax returns and then you did them for low income individuals. The proper spin could be put on this to make it sound more personal finance related. Or maybe you could sign up for this program now.
What about your current work, if you're employed? What practice area does it involve? Is any of it somewhat related to estates or personal finance? Trust account management, exemption planning, risk mitigation from a financial perspective, tax work?
What about extra-curricular activities, clubs, or hobbies? Ever serve as treasurer of an organization? Ever do any fundraisers? Ever work for any non-profits, even if its volunteer work, or for nursing/retirement homes? If you're looking to get into this area anyway, Order of the Eastern Star (if you qualify) may be a good club to join.
All ideas, hopefully it helps you somehow. Ideally you'd have 3 years working for an estate planning law firm, or a cpa. But if not, try and find as many connections that you can and emphasize them. I'd show your enthusiasm for the field in your cover letter. That type of business involves substantial networking and sales like tactics, so I'd be prepared to sell yourself. If you can get enough connections to the financial world across, you could get an interview.
Go get 'em!