Give it a try. Every optin list provider gives a set of code to paste into your website. You can paste it anywhere you like. I put it on my contact page and on the end of most posts. They call the code a trip wire because you can scatter the code throughout your website to encourage people to sign in. When using visual editing I usually type 3 *** where I want to insert the code. Then I go to text edit find and remove the *** and replace it with the sign in code.
Figuring out when your visitor is ready to convert depends on your website viewers’ behavior, so you’ll want to conduct A/B testing to determine where you need to place your CTA. Does it work best towards the bottom of a blog page, when it slides out to the right, or does it get higher conversions at the beginning of the page, sliding out from the left?
Some ad platforms will ask more of your landing pages than others, when running ads. For example, AdWords is much stricter, when compared to Facebook. AdWords typically requires that you do not have a ‘thin,’ site that is designed solely to collect leads. Because of this it might be a good idea to focus on using Facebook or Twitter, to begin with.