yes, it can be done, how to do it depends on menu configuration.
if PageMenu is configured like this in layout.master:
<portal:pagemenu id="PageMenu1" runat="server" useflexmenu="true"></portal:pagemenu>
then in theme.skin you can make it show all pages by removing the highlighted line below or changing it to -1:
<portal:FlexMenu runat="server" SkinID="PageMenu"
ContainerElement="div"
ContainerCssClass="art-box art-vmenublock"
RootUlCssClass="art-vmenu"
DescriptionCssClass=""
ChildContainerElement=""
ChildContainerCssClass=""
RootLevelLiCssClass=""
ItemDepthCssPrefix=""
ParentLiCssClass=""
StartingNodeOffset="0"
MaxDataBindDepth="-1"
RenderDescription="false"
UlSelectedCssClass="active"
LiSelectedCssClass=""
AnchorSelectedCssClass="active"
AnchorChildSelectedCssClass="active"
UlChildSelectedCssClass="active"
/>