How to leave joint tenancy property to some who is not a co-joint tenant.

I am a lawyer in CT and practice in this area of the law.  I suggest that you convey your interest in the property to a limited liability company that you and your fiance are members of.  this way, if you pass away, the LLC will continue to exist and your fiance will have the benefit of being a joint owner of the property.  I suggest hiring a lawyer to help you set up the LLC and quit claim deed to effectuate the transfer.

What type of joint tenancy is this - tenants in common (TIC) or joint tenants with right of survivorship (JTWROS)?

If you have the latter, then upon your death the other joint tenants will take over your share by operation of law; you cannot bequeath, sell or otherwise transfer or encumber your share (at least not without the permission of all the other joint tenants).

If, on the other hand, you hold title to the property as TIC, then your share is freely transferable; you do not need the permission of the other joint tenants to convey it.

Note:  If your deed is silent as to whether your are a JTWROS or a TIC, the law presumes that you are a TIC.