See http://hackingdistributed.com/2016/02/26/how-to-implement-secure-bitcoin-vaults/ http://hackingdistributed.com/2016/02/26/how-to-implement-se... for a write

See http://hackingdistributed.com/2016/02/26/how-to-implement-secure-bitcoin-vaults/ http://hackingdistributed.com/2016/02/26/how-to-implement-se... for a write-up on (I think) the exact thing you propose.