Without testing: Create a custom "list create block" in a variable. Append to this variable all the definitions you want to have. Call listbuilder with this variable.
Here is some dummy code:
if $admin_p {
set element_code "[list label "delete" ....]\n"
} else {
set element_code ""
}
Look at the elements definition in file-storage/www/folder-chunk.tcl.
Before the last "]" you just add "$element_code" on a new line, and off you (should) go.
