Follow Up Letter

What are everyones thoughts on this situation... Interviewed with a small but prestigious boutique in January for a position that wasn't open at the time. The CEO of the firm is a family friend and had me go through their traditional 8 hour super day. It is somewhat of an odd situation because I was essentially interviewing for a full time position that doesn't exist, at least not yet.

Since then I have had been selected to an international case competition team by my university. Would it be a good idea to send him a hand written letter thanking him once again for the opportunity while emphasizing my strong interest in the firm? I figured I'd also attach my updated resume in the letter.

Thank you all in advance, your time and insight are very much appreciated.