changing configure --prefix later?

OK, I'm building ghc-5.04.3 freshly from source, but when running
./configure initially, I forgot to use the --prefix= option to set the
final installation location.  Now, after fourteen hours of building,
I use `make install' and discover the mistake.  :-(  How can I recover
the situation?

I tried re-running ./configure with the intended --prefix option.
No joy.  I tried deleting config.cache first, then re-running
configure, and then `make install'.  In all cases, the installed
ghc driver script still points to the wrong place (/usr/local/...)
If I edit the installed driver script to point to the right location,
I get errors later in the installation that the pointed-to binary
doesn't exist.  And indeed it doesn't, because the scripts are
installed *before* the binaries they point to, but the installation
process itself seems to call GHC to build something.  In this case,
the error is:

    ------------------------------------------------------------------------
    ==fptools== make install -wr;
     in /grp/haskell/ghc-5.04.3/ghc/compiler
    ------------------------------------------------------------------------
    /export/home/malcolm/bin/ghc -ldl -cpp -fglasgow-exts -Rghc-timing -I. 
-IcodeGen -InativeGen -Iparser 
-iutils:basicTypes:types:hsSyn:prelude:rename:typecheck:deSugar:coreSyn:specialise:simplCore:stranal:stgSyn:simplStg:codeGen:absCSyn:main:profiling:parser:usageSP:cprAnalysis:compMan:ndpFlatten:nativeGen
 -package concurrent -package posix -package util -recomp -Rghc-timing -H16M 
'-#include "hschooks.h"' -O    -c main/Config.hs -o main/Config.o

    /export/home/malcolm/bin/ghc: /usr/local/lib/ghc-5.04.3/ghc-5.04.3:
    not found

So, I appear to be stuck in catch-22.  Any ideas?
Regards,
    Malcolm