process substitution question

[Paul Lew <remove-this-part-paullew@xxxxxxxxx>]

I have been using the =(cmd) for process substitution and now I have
a case where I am not sure how to specify this properly.  There is
a command which take input file with format:

    > cmd file:xyz

where 'xyz' is the filename.  I would like to subsitute the file name
'xyz' above with =(command),
i.e.,

    > cmd file:=(command)

What is the best way doing this?  Thanks in advance.