Using variables in registered toolbar

I'm trying to create my own toolbar using the "Layout.toolbars" file located under ".cadence/dfII/toolbars/byApplication". I'm facing a problem creating combo box that grabs information from tech library. It seems to be that the "value" and "items" field of combo box needs to be hardcoded with strings or list of strings.

 For example, the following is defined in "Layout.toolbars":

 (
        nil
        name myToolbar
        text "My Toolbar"
        items (
            (
                nil
                type            comboBox
                name            lebComboBox
                tooltip         "Combo box's tooltip"
                prompt            "Combo box:"
                items            myGetComboItems()
                value            myGetComboDefaultValue()
                callback        "myComboBoxCB()"
                width           100
                editable        nil
            )
)

When Cadence try to load the toolbar, it will complain that:

*Error* hiCreateToolbarComboBox:: ?items must be a list of strings, or nil

Same for the ?value field, it needs to be a hardcoded string. How can I get around this? I know I could use hiCreateToolbar() and hiPlaceToolbar() to create combo box with variable items and default value, but if I do it that way the toolbar won't be registered properly i.e. cannot be saved as part of a workspace.

Any feedback will be greatly appreciated.