Own opclass and LIKE problem again!

Hi!

Thank you very much the answers for my previous 'Multi ordered select
and indexing' question! I tried your suggestions, and those are working
well. We found a problem when used '(-col2)' instead of 'col2 DESC'.
This solution working as a functional index and in our experience when
the planner evaluates the cost of using this functional index, it uses
0.5% of the table's size. Usually this estimate is bad, and the query is
slow. Why is it working such? Preferably should I ask this on the
HACKERS or PERFORMANCE list?

But my main question how can I force the LIKE operator for using my own
operator class. I can create own LIKE operator, but it won't use my
reverse order operator class (and its indexes). How can I exchange the
standard LIKE operator with my own, which use my special reverse order
indexes?

For examle: (~~ means LIKE) col ~~ 'asd%'   working as  ((col >= 'asd'::text) AND (col <
'ase'::text))
I'd like to see the next: col /~~ 'asd%'    working as  ((col />= 'asd'::text) AND (col /<
'ase'::text))

Can somebody help us?

Thanks in advance.
Antal Attila