They are offering it, the 'lack of response'. You can choose to drop people and then been strictly interpretive of their requests (or lack there of) for followup. So if you leave a meeting and there are no next steps, just stop talking. Later at your series B you can offer to bring them up to date on your current plans.

Understand that some (many?) VC's understand that saying "no" explicitly can hurt your prospects with other VCs (you will be asked to explain why that other VC said "No" which is impossible to do usually because you don't have the complete picture). So they let it drift quietly silent and understand when "you are really busy and might not get back to them for a while."

Agreed. You can basically stop trying to prompt them to follow up with you (since they are non-responsive / won't suggest next steps typically in this scenario).

Another tough thing to balance is the flip of this - how to politely drop a VC you do not want to talk to further, who is interested in your company and knows you are fundraising...

"I'll take that as a no. But hey, thanks for your interest. "

["that" being a wishy-washy response, no contact for weeks etc]

Here's a post I wrote about this ages ago: http://www.derekscruggs.com/slow-turndowns-bad-up-front-cont...

I've found that giving people permission to say "no" is powerful in many contexts, not just sales.