Global Tracking Pixel

sure you can do it through an iframe pretty easily.

Just place a pixel where you need to like this

<iframe width='1' height='1' frameborder='0' src='https://yourdomainhere.com/pixels.php'></iframe>

Then make a file on you server called pixels.php and put your pixel code in it.

Pretty sure that should work.

Directtrack offers a version of the platform catering to affiliates, which offers a global third party pixel. Javacript or an iframe.

Pm me for details

I worked with a number of offers where I could only place an image pixel rather than an iframe - I ended up custom coding a quick & dirty system for pixel placement. You can either code this yourself or hire someone to do this, probably on the cheap.

Clicks from source X get sent to http://trackingdomain/?campaign=1&source=X
Cookie is set to Campaign=1, Source=X
Pixel is placed as an image - http://trackingdomain/thepixel.php
Pixel script looks up cookie set on the click (campaign & source) and checks with database to see which image pixel to redirect to
Pixel script throws a 301 redirect to http://advertisingsource/pixels/blahblah.gif
Advertising source pixel records the sale

iframes are generally an easier option (as Jason mentioned) - but in some rare cases where you can't place an iframe pixel, the solution that I described above will work very well.