External Links add code to open within an iframe

Our client requested that all their external links open with a top frame with their logo and and back button to their website. Now we got that part working my dilemma is how can I implement this code to all external links without doing it manually? I need to add if before the “http//link”. There’s two places where we are using external links, one is the RSS feeds from other websites (i’m using a plugin to display them on the website). And also I need to add it to links I have imputed using the “links” section under the WP dashboard. Is there a script or something similar that will allow me to add this code to all the external links?

Thanks in advance for your guys help!