I just realized that the solution is not as good as it seemed to be. It seems that if I use a markup, the distance between subsequent crotchets won't be the same, as the first crotchet of the measure (the one that is represented by the markup) will be placed a little more left than it should be. So I need a solution where the actual bar lines would move 'a bit to the right' in order to be in sync with the first notehead in the measure.
What about using proportional spacing and then moving the bar line slightly to the right? Something like this:
\version "2.15.30"
{
\time 2/4
\override Stem #'stencil = #point-stencil
d' d'
\once \override Staff.BarLine #'extra-offset = #'(1.5 . 0)
d' d'
}
\layout {
\context {
\Score
\override SpacingSpanner #'strict-note-spacing = ##t
proportionalNotationDuration = #(ly:make-moment 1 8)
}
\context {
\Staff
\remove "Time_signature_engraver"
}
}