Hari om,
That is a great news that in some western country still people remembered our culture and performing such a great Anushthana,yeah its pity that it's not possible there to get help of any bonafied pandit who could perform this yagya for you there.
It has to be 10% yagya of the total number of chanting of mantra,and 10% of Havan "Tarpan" should be done,next 10% of Tarpan "Marjan" should be perform,Finally 10% of "Marjans" Brahman Bhoj and "daan" has to be done.This is the method...
and if someone unable to do all these rituals then he should do "thrice" Japa.i mean if you people are doing 100,000 of japa then for completing this anushthana without any yagya you people should do "300,000 japa.
Hope you have understood this.
Regards
swami Nishchal anand ji