how to set a partial measure after the beginning of a piece?

[Marc Mouries]

I checked the doc here:

http://lilypond.org/doc/v2.12/Documentation/user/lilypond/Displaying-rhythms

and it says: "partial command is intended to be used only at the beginning of a piece.  If you use it after the beginning, some odd warnings may occur. "

Any pointer about how to achieve this?

The fiddle piece is composed of 2 parts

part 1 = 4/4 | partial 4  |  notes  | measure  with 3 beats :|

part 2 =          partial 4 |  partial 4  |  notes  | measure  with 3 beats :|