Incrementing field in Mailing Labels - part 2

[dennis]

I have already asked about an incrementing field in another
thread. Graham was kind enough to answer. I have a followup
question please:

Can I have a USER INPUT type of field to "seed" the
FUNCTION, so that I might use:

=({SEQ label} + MySeed)

So that if a user enters 1000, the first field sequence
number is 1001?"

I don't really understand how to use that type of input
yet, so I'd also like to know how I can "hide" that field
in the document, but have it come up for user-entry when
ready to print (or when opening the doc, it really doesn't
matter when).

Thanks!