prickly problem :P i've no decent solution i concur.
the biggest challenge is to consider several sides of the issues, especially with him as a colleague, where harsh means are often inappropriate. cannot punch him, cannot kick him, cannot do anything that affect one's image in the office as well.. i.e. claim to be a les etc..
sometimes one or two of my female friends would approach me with similar problems but not in a working context, but in school, almost the same scenario, but most of these times i would actually act as their "bouncer" or negotiator, and i would speak to those guys on their behalf on what actually is going on and where everything is going.
get an older man (friend) to look him up and tell him that you are not interested in anything along those lines, and that he should leave you alone, at the same time you do not want to spoil the working relations as a colleague.
something along the lines of :
old man camping outside office after work and approach the guy as he is about to leave
old man : hi, is this mr XXXxx
xxxxx : yes i am.. you are?
old man : i'm here to talk to you abt.. jeanie blahblahblahblah..she finds it hard to get things across from her position and i am here to clarify some issues with you and hopefully to seek a resolution over them. blahblahblahblah..
chezburgr i can haz?
c'mon jeanie count your blessings... some girls die as virgins..
while some even dont feel loved...some dont even felt being pursued..
in you ur pursuit of happiness, maybe put him in the last option lor..
when he first intro himself to me, he was such a gentleman...
in fact, the impression he struck to me was really good.
but as time goes by....
ORTEGA:if you remember last year valentine, he was the one who gave me the flowers and i did ask you wat to do with it...remember?