You can use CEikSpacer which is an invisible control that is used to provide a space between visible controls. Include it in the resource entry of your TOOLBAND or TOOLBAR.
TBAR_CTRL
{
type = EEikCtSpacer;
id=0;
flags=0;
length=0;
control = SPACER
{
width=10;
height=10;
color=0; // clear
};
},