Short of rain, automatic system or a friend coming over to water for you, I don't know of wnything that will keep it wet all week. A few day maybe.

I don't know from experience but is the shrub that fragile? A week between waterings seems survivable to me?

I don't know that much about this shrub -- I do know that I'd keep any new shrub fairly moist, and this one requires moisture, so I'm afraid to chance it drying out after only a month in the ground. I found a soaker hose that's designed for a single shrub, so I guess I'll get a timer and try that.

I have Kirengishoma lalmata and koreana. Last year was dry and they did not perform well, but they survived, this year they are gorgeous. So get them established and give them extra water as one would for Astilbes, but don't worry about it too much.