Hiding the Taskbar Label Only for Specific Applications
I found a solution! This little application allows lables to be hidden per application ID. I think it is exactly what you and I have been looking for.
http://rammichael.com/7-taskbar-tweaker
The state of the taskbar, whether "Icons only", "Icons when full", or "Icon+label", is internally called the "glom" level, and is dictated by the registry key HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced\TaskbarGlomLevel
where the possible values are 0, 1, and 2 respectively. Unfortunately this is a taskbar-wide setting and there is no finer grain control to do what you want, which would be to make an icon-ified application wider to display title text, or an icon+text taskbar button smaller to hide the title text.
Not exactly what you're looking for, but 7stacks from Alastria Software can put shortcuts for several applications in 1 taskbar icon, using "stacks" (à la Mac OS X).
7stacks is an easy to use, free app that lets Windows 7 (and Vista and XP) users have "stacks" of icons in their Taskbar (in 7) or QuickLaunch Toolbar (in Vista and XP). By using stacks, users can reduce icon clutter, and combine a group of related icons into a single icon. For instance, if you use application suites such as Microsoft Office, OpenOffice, or Adobe CS4, you can have all the suite's icons combined into one icon!
I don't have access to my Windows 7 box now but you could try to specify an empty name for a new stack, use a custom icon and pin it to the taskbar.