If you go into your InDesign application folder, under Scripts/in5_v2/Startup Scripts/ and open init_in5.jsx.
On line 18, replace the following:
if(!app.scriptMenuActions.itemByName(markThumbTitle).isValid){
With:
if(true){
And restart InDesign, it should appear.
Please let me know either way. A check was added to ensure that v2 didn't conflict with v1, but it seems to be preventing this option from appearing in some cases.