I know the names of the symlinks involved, so in principle I could put them in the transfer mask, but there are thousands (30000+) of symlinks involved and I rather doubt the field will accept that much text. It would be very useful if there was an option, therefore, to derive the mask from the contents of an arbitrary sized mask file, one rule per line and/or semicolon-delimited as usual. Then the user just needs to keep the mask file up to date, and only the right files get transferred. The mask file could be local or remote, potentially. How efficiently this could be implemented is another matter of course - though it's got to be quicker than downloading gigabytes of unwanted files!
Useful idea, or something already done that I just haven't found yet?