You can perform a uuencode:
IN: scratchpad "Factor" string>uu print begin &1F%C=&]R end
...and also a uudecode:
IN: scratchpad """ begin 644 factor.txt &1F%C=&]R end """ uu>string . "Factor"
Right now, it operates on text directly and doesn't preserve the file name and permissions in the
begin header, but that would be an easy improvement.
The code for this is available in the development version of Factor.