How to prevent creation of a second Icon in Windows TaskBar after start?

I use (among others) Thunderbird and Firefox from PortableApps.

I pinned the start executable (e.g. ThunderbirdPortable.exe) to my Windows 7 TaskBar.

However when I click on it a second Icon appears on TaskBar. I guess its the actual target Thunderbird.

"Normally" (for other programs) the first icon remains the only icon representing the running program.

Is there a way to handle PortableApps programs in the same way?
I want only ONE icon in TaskBar after start.

Can I somehow avoid a click on ThunderbirdPortable.exe and start target Thunderbird.exe directly (with cmdline parameters)?