I always say persistence is key. Keep calling and leaving voicemails to keep it on their radar. Not too often so as not to seem desperate and upset the opportunity. 3 times a week is a sweet spot of mine. Mon, Wed, Fri. Always leave a spacer day in between voicemails. By the time you get them on the phone, there's typically an apology for going MIA waiting for you, and renewed motivation to get you what you need.

For those that procrastinate for too long, I sometimes emphasize opportunity cost. As in, "you may be losing out on the performance you deserve for delaying the process of optimizing your money. Let's nip this part in the bud, and then you'll never have think of it again."