If the caller is on hold, it isn’t a blind transfer, but an attended transfer. How are you initiating the transfer? If you do a SIP native transfer, some phones actually implement blind transfers as attended ones; they dial the new number on a second “line”, but then issue the REFER/Replaces automatically when the callee answers.
For a true blind transfer, whether a SIP native one or an Asterisk features one, if I remember correctly, the transferor is released immediately and the call is put into the same dialplan as if it had originated directly from the caller (although I think it may be on a Local channel).
If it is really a native attended transfer, Asterisk doesn’t know that it is a transfer until after the call succeeds. For a blind transfer, I guess it would be possible to call back to the extension or caller ID, but I don’t think the FreePBX dialplan has support for that.