Enriching gene copy no.

[G]

Hi
I,m trying to study induced mutations in genomic DNA by a PCR technique.
The problem I have is that the mutation rate is about 10 to the power -7-8,
but this would involve putting 1mg of DNA into the PCR reaction! I thought  
that I could cut the gene I'm interested in out of a gel after digestion
with an enzyme which cuts 3' and 5'. My question is has anyone tried this
and how can I optimise my digestion and recovery of my fragment.
Cheers
Gareth