How to dynamically control the size of a HIT in Amazon Mechanical Turk?

Question

I'm posting search relevance evaluation task. Basically I'll provide a query and a bunch of URLs which may or may not be relevant. Turkers need point out which ones are relevant and which ones are not.

To not to bother Turkers to click on the url and comme back again,I've put "iframe"s in the HIT. But since there are 25 urls in a HIT, it's loading slow and for some queries there aren't enough pages to display (15 to 25 pages each HIT).

So, is there anyway I can dynamically control the number of "iframe"s ??

Thanks,