but cannot hope to fill up the beds with plants in a short
period,


Well you could if you sowed seed either stuff like sweet William,
forget-me-not, stock which will grow into small plants now and be ready
to flower next spring.
You could put in bulbs, or some of the end of season cheap bedding to
fill gaps
You could even try sowing some vegetables in the gaps just to cover the
ground

In a recently visited garden the very keen and expert gardener had
covered his island beds with gravel (the small pea shingle stuff) and
planted through, he assured us it had dissuaded his neighbours 3 cats.
--
Janet Tweedy
Amersham Gardening Association
http://www.amersham-gardening.net