I think you will need to write your own 'quasi' FTP Daemon
that runs under CICS.
You will need to write the code to use the Sockets API functions available via the z/OS Communications Server.
I have written (a couple of years ago) CICS code, using the Sockets API similar to FTP functionality. Of course you will need to follow the guidlines for FTP.
Reference material (Communications Server) can be found at the following IBM Bookshelf;
There you will want to most likely first read the z/OS V1R4.0 Communications Server IP API Guide - this is the guide for all langauage references. (C, Assember Macro Interface and the CALL Interface - supporting ASSEMBLER, COBOL and PL/1)
Another approach (I have not experimented with this) is possibly to LINK to the FTP module itself, but again like I mentioned, I never experimented with this approach to actually see if it is indeed a working solution.
Yet another approach - Use CICS as the catalyst in which you can submit (from CICS) a BATCH job which itself then uses FTP (in batch mode) ? - Thats a design question you can only answer if, infact you can use this approach.
In any event, some R&D will be required here - the above URL to the IBM bookshelf (z/OS 1.4) I am sure is still good.
Good Luck