Yes, you're on the right track
Ok, what you need to do step by step:
Add the "glass" item to the items.items file.
ITEM
{
CURSOR_COMBINED = FALSE
NAME = "glass"
IMAGE = "not important"
CURSOR = "some_image.png"
CURSOR_HOVER = "some_other_image.png"
}
Create a button on the inventory window. If I understand it correctly, you already have it. Let's assume the button is called "glass_button". Its definition should be something like this (hidden inside the inventory definition file):
BUTTON
{
NAME = "glass_button"
PARENT_NOTIFY = TRUE
IMAGE = "some_image_again.png"
X = 100
Y = 200
...
}
Now, in the script attached to the inventory window, add the following piece code:
on "glass_button"
{
Game.SelectedItem = "glass";
}
This means, if the glass button is pressed, make our dummy item selected (the cursor changes).
And that's it! All you need to do now is to handle when the player clicks some regular inventory item with a magnifying glass selected.
In a script attached to each inventory item add the event handler:
on "glass"
{
actor.Talk("Put an item description here.");
}