Yes, you can purchase by using the monthly instalment method. The advantage of this method is you can min. the risk as it used the weighted average method for the purchasing price.
If you have BOC security account, you can adjust your contribution on monthly basis (from min HK$1000 to max HK$20000). When using the monthly instalment method, bank will charge a handling fee per each contribution. However, no bank charge on receiving the dividend (for BOC only, as I am not sure the other banks). So, this method is very suitable for those shares who distribute dividend 4 times per year.