You pretty much have it. Direct your servicer to transfer your after-tax contributions to a Roth IRA. For my servicer (Fidelity), it's a phone call once a year - they have done this many, many times and they'll know exactly what to do. Very easy, only takes a few minutes.
Any earnings on the money are taxable at your marginal tax rate, but not subject to the 10% early withdrawal penalty. At the end of the year they'll send you a 1099-R showing the distribution and also the taxable amount. I think it's also possible (and legal) for them to separate out the earnings on the after-tax contributions, so you can transfer to an IRA and not pay taxes up-front on the distribution. I've always just paid the tax on the (relatively small) amount rather than roll it over, but that may be something that's an option as well.