Skip indetation in Emacs vhdl-mode

Hi all,
Exist any simple possibility in Emacs (vhdl-mode) to skip indentation
for particular block of code? The best would be to possible to include
any directive behind comment sign. See just a brief example lower.

What beautify function does

A.<= B & C &
B_int & C_int;

What is required

-- dont_indent_start
A <= B & C &
B_int & C_int;
-- dont_indent_end

Thanx for any advice.

Xipn