Tracking adwords with modrewrite?

[planbeta]

Hello I'd like to be able to track which keywords are getting which sales from adwords to an affiliate site. The affiliate site has SOME referal detail but it doesn't show the query string ie. only shows this as the referring URL:

[google.com...]

Without the extra query string, with the keyword in, I can't identify which keyword was responsible for which sale.

I've tried making a redirect script using ModRewrite, eg. for an adword with "keyword phrase" as the keyword when someone goes clicks on it, instead of sending them directly to the affiliate site I send them here:

[mysite.com...]

I then just set up ModRewrite to redirect any ".shtml" pages to redirect to the affiliate site:

RewriteRule ^(.*)\.shtml$ [myaffsite.com...] [L,R]

I hoped this would pass on this url as the referring url:

[mysite.com...]

but this shows the referral as "NO DATA" in the stats
.

Is there anyway to do this? Maybe using some PHP in combo with ModRewrite?

Bet that doesn't make any sense at all, does it!? ;P

Cheers

Chris