Complicated split test question

I'm having trouble setting up a split test - where I need to test multiple landing pages and sales letters at the same time.

I need to split test 2 different landing pages, plus 3 different offer pages

(first the prospect will land on either of the landing pages which are both opt-in pages. After filling out the opt-in form, they need to go to 1 of 3 offer/sales letter pages)

Here's the issue I'm running into.

I have the test set up to rotate between the 2 different landing pages, however once they opt-in on either of the 2 landing pages, I then need to rotate between 3 different offer pages.

I tried to set this up having the 'conversion page' for the optin/landing page be a PHP file with both the conversion code (for the landing page split test) on it, plus a redirect to the URL for the split test on the 3 offer pages.

The problem is, that php file won't do both actions. If the redirect code is before the conversion tracking code, it doesn't track the conversions

If the conversion tracking code comes first, it doesn't ever redirect

Does anyone here know how I can do this split test with the 2 different opt-in pages then 3 different offer pages?