Multihomed to 2 ISPs - Load Balance?

[John Smith <jsmith4112003 () yahoo co uk>]

Hi Fellow Nanogers:
 
I searched the archives and could not find anything that really matches with my requirement. I have been stalking this 
mailing list since quite some time and its extremely rare that i post.
 
We are multihomed and connected to the Internet via two upstream providers. The initial idea was to get more bandwidth 
and redundancy. Now, we're past this stage and want to try out something different.
 
Please note that we also provide transit services to a few downstream providers.
 
We wish to load balance the traffic for a block/range of IP addresses that we learn via BGP4 from our two upstream 
providers. The problem is that my favorite vendor does not let me install ECMP routes in case of routes learnt from 
extrnal BGP peers. Assuming that we are able to install EBGP ECMP routes, how do we advertise this information to our 
downstream peers? As far as my working knowledge of BGP4 goes, it wouldnt let me do this.
 
I wish to understand how other network operators do this?
 
You can, if you wish, send me a message offline and i will collate all the information that i receive and send out a 
consolidated reply for the benefit of others to this mailing list.
 
Thanks,
John