Create dynamic gateway with reserved public ip

Can I assign reserved ip to dynamic gateway in azure vnet ?

Trying to setup multi site VPN where on premise has two physical VPN locations. Need to create dynamic gateway as per article http://msdn.microsoft.com/en-us/library/azure/dn690124.aspx .

Just worrying if after creating the dynamic gateway, will new Ip get assigned any time ? Till what time the IP of dynamic gateway will remain same ?

Thanks,

Subodh