Long-time stalker; first-time poster. Thanks for all the advice in the past guys - much appreciated.
Given the potential for angst and loss of match control if things go wrong, my inclination would be to step in. However - and I don't think that anyone has mentioned this yet - remember this is an indirect free kick. Keep your arm down as an insurance policy. If the attacking team go quickly and the GK and his defenders are clearly not ready, quick blips on the whistle and apologies all round, "Sorry guys, I wasn't ready and didn't have my arm up to show it was indirect. Let's go again, and it's on the whistle this time"