xgettext & multiline string literals

First of all hello to this list!

I am searching for this quite some time, but still could not find any 
answer.
I use gettext in my C programs with no problems some time now. So
I decided to do the same with my web projects.
It was a nearly painless start, with only one exception. I am not able
to use multiline string literals for slightly longer texts in PHP.

In C i can use the following:

_("This is just a slightly longer "
  "text for demontration purpose");

To split one long string into (what i called) a multiline string literal. 
This
works perfectly, at least with gcc and xgettext does extract the whole
string (both lines) as a key.
In PHP this is not possible at all because it simply does not allow this
syntactically.
So i tried the following in PHP:

_("This is just a slightly longer " .
  "text for demontration purpose");

But that is not understood by xgettext. The .po file does only 
contain the first row of the string as a key.

Has anyone any solution for this?


Best regards
   Georg Steffers