It's a slippery slope of course. Since money is fungible, premiums that go to an insurer to pay for a policy that doesn't cover abortions almost certainly goes into the pool of cash that the insurer would use to pay abortion claims from other policyholders whose policies do cover abortion. So to avoid "funding" abortion, you'd need to obtain a policy from insurers who refuse to write any abortion coverage at all.
But let's not get too far afield from the richness of the irony that while the Republican Party has defined itself as the anti-abortion party it has in fact been providing insurance coverage for abortions to its employees. It reinforces what we've all known for a long time: grafted onto the genuine and sincere questions about when life begins and where to draw the line between the state and the uterus is the ugly calculation that so long as affluent white women have access to abortions a whole lot of political points can be scored in denying abortions to poor and minority women.