Deputy services will do that for you - bid on YJ 
actions on your behalf, while asking for 
commission for their services.  Some services 
are:  Rinkya, Celga, Anime Chaos, Hobby Shop K, 
and I'm sure there others, those are the only 
ones I can think of at this time.  I have only 
used the first two, and I have had no problems 
with either one.  Celga accepts newbies but 
usually bids several hours prior to end of 
auction (unless you use their Gold service).  
Rinkya might have a registration period but lets 
you bid real time.