how to create a dynamic mark "pp sempre"?

[Michael Kiermaier]

I want to have a dynamic mark "pp sempre".

On
http://lilypond.org/doc/v2.8/Documentation/user/lilypond/New-dynamic-marks.html#New-dynamic-marks
the manual shows two ways to create new dynamic marks:

1)
Dynamic marks consisting only of the dynamic-mark-letters f,m,p,r,s and z, s, 
so "pp sempre" cannot be done.


2)
New dynamic marks using the markup command:

For example:
ppsempre = \markup {  \dynamic "pp" \italic "sempre" }

And using it:
c-\markup

But this is not a real dynamic mark, because for example, crescendo marks do 
not hook to it.


How do I get a dynamic mark "pp sempre" that behaves like the usual dynamic 
marks?
Thanks,

~michael