Method to change browser User Agent based on site

Dolphin Browser can be configured to act as one of a range of User Agents (Android, (full) Desktop, other phones...). But this is for every site visited until you want to change the settings to some other agent (browser type). Some sites have better mobile versions than others. I wondered if there is a feature/plugin on this or another Android browser to set the Agent individually for a range certain sites, e.g.: - facebook.com (full Desktop - because mobile edition is limited) - nationalrail.co.uk (Android, quicker than Desktop and easier to manage) etc. This would then 'trick' the website to load the site in a version as specified.