orphans and widows

Hello.

In my document, I have a lot of screenshot pictures (It's a manual).

Sometime (really often in fact) I have as PDF result something like  
that :

--------------------------------------------
some interesting text...

Picture

Some other test which explain the next picture
<big space but to small to put the next picture>
<generated page break>
Picture

other text

-----------------------------------------

And I would like to have

--------------------------------------------
some interesting text...

Picture


<big space>
<generated page break>
Some other test which explain the next picture
Picture

other text

-----------------------------------------

I've put in my custom stylesheet an orphan and widows attribute-set :

     <xsl:attribute-set name="root.properties">
         <xsl:attribute name="widows">4</xsl:attribute>
         <xsl:attribute name="orphans">4</xsl:attribute>
     </xsl:attribute-set>

But with no result. I kown that FOP doesn't implement this feature,  
but I use XEP (who does).

So the question is : how can I have the good result ?

Thanks in advance.
Jacques