insert element in IBrokers/XTS time series?

Hi all,

Let's say I have the following timeseres in IBrokers and XTS:

2009-06-25 ? ? ?18038 ? ? ?18350 ? ? 18011 ? ? ? 18327 ? ? ? ? 5396 ? ? 18183
2009-06-26 ? ? ?18420 ? ? ?18708 ? ? 18331 ? ? ? 18515 ? ? ? ? 7367 ? ? 18499
2009-06-29 ? ? ?18546 ? ? ?18688 ? ? 18423 ? ? ? 18577 ? ? ? ?28728 ? ? 18555
2009-07-03 ? ? ?17951 ? ? ?18198 ? ? 17866 ? ? ? 18149 ? ? ? ?38019 ? ? 18059

I want to add a few more rows, indexed by

"2009-06-30", "2009-07-01", "2009-07-02", and using NA's,

I did the following:

myhist["2009-07-01",]=c(NA, NA, NA, NA, NA, NA, NA, NA)

But it didn't really work.

What's the good way to insert missing points in time series?

Thanks!