[gentoo-user] Creating an firmware image from a too large microSDcard...?

Hi,

to post a firmware image of my embedded linux computer
to a friend I want to size it down.

System wise I did that already (only the really necessary
stuff of Gentoo plus some configuration and addons related
to the embedded system)...the problem comes with the size of
the microSDcard I use: 32 GB....

The microSDcard (source) has two partitions (boot + the rest).
The boot partition is the first partition and it is of a fixed
and tiny size. The second partition contains the "rest": Gentoo.
Currently the used space of this partition is also small.

The image needs to be of a format, which makes
it possble to 'dd' it onto a microSDcard (target) and afterwards use
g/parted to resize/expand the second partition to the end
of the microSDcard to get all storage space available.

If I dd the source into an image I get all those zeroes also and
the image only will fit onto a microSDcard (target) of at least
the same size.

If I dd each partition separately I get two files and the partition
table is not copied...may be technically possible but not user
friendly.

How can I manage to get an image from my microSDcard (source), which
only consists of the used space in a way that it can be put onto 
another microSDcard (target) in the waay described above?

How can I acchieve that magic ?  ;) :)

Thank you very much in advance for any help!
Best regards,
Meino