I got kind of the same problem with icons in a drop-down list.
I finally switched to use a slider + label in the libAddonMenu settings instead of a drop down.
I'm still waiting for LAM to update the drop down box with a scrollbar at the popup
Wykkyd got such a control in his libraries (at Wykkyd Full Immetsion, the emotes list) and I tried to adopt it to LAM already but failed