Different markups for odd and even lyrics lines / stanzas

[Specken Flecken]

Dear lilypond people,

Marek from the bug squad suggested, I should post this question here.
Does someone know a solution for the following problem:

I want to distinguish odd and even lyrics lines, i.e. stanzas. I can
think of 3 variants:

 1. Colored resp. light gray background,
 2. a vertical line after each even numbered stanza  or
 3. extra vertical spacing after each even numbered stanza.

I would be grateful for suggestions how to accomplish this, e.g.
using scheme.

Best regards,
SpeckFleck