I had exact the same problem with my USB hw.

So I worte two apps one for the update linked to 0x000
and a second one (the real app) linked to 0x2000.

After some tests with the std proc for relocating the irq vectors I used another way ..

Take a look at :
http://www.8052.com/forum/read.phtml?id=13141

I found this trick some years ago in a assembler module
and adapted it to C.
Hope this helps

Thomas