I'd be against building TN into Gluttony. Those bursts of back to back positionals are actually really fun. The workaround to Gluttony drift is to just have it start at one charge out of combat, but have a maximum capacity of two charges. The problem with starting at two charges is that you're not really going to get to Double Enshroud in time in your opener, even if they gave you tools to do so. The vast majority of jobs are driven by timers without real resource management, so they will set up their burst windows relatively quickly and you need to sync up with that. You don't really have time to delay five additional GCDs before starting burst. You'd nearly almost have to start off with the resources on entering combat.
You don't want to extend the length of your rotation during Double Enshroud, because you'll likely push your Communio out of the window. But if it's just for the 1 minute Enshroud, there are plenty of ways you can already add in an extra Weaponskill GCD to avoid clipping. You can SoD as filler at any point during Enshroud. You can also use HM the same way, if you like, although it's all a bit redundant in this sort of situation. I would avoid Enhanced Harpe in that case when you already have access to both HM and Communio, since it is still a potency loss if you have the option of melee uptime.
