Pidgin has a feature to set the placement of tabs. Tools/Preferences/Interface/Placement I would like the left/right sides to be displayed like in Gigolo rather than the XChat style of Pidgin.
You can patch the code.
Concerning to Pidgin, I want to correct myself, there is an ability to use horizontal/vertical when at the left/right sides. I think that what mostly matters is to add the bottom placement.