Unfortunately for him, the religion he believes in, doesn't allow it. Fortunately for him, he doesn't have a clue what his religion allows and what it doesn't.In fact, in my eyes, he is a better human being for doing so.
Consider this statement of his for eg.
The pagans of Mecca approached the prophet (saw) with a similar proposal. They first offered him 50-50. They said you worhip our gods for one day and we will worship your God for one day. The prophet (saw) refused. They then changed it to you worship our Gods for 1 day and we worship your God for a week. It went upto a year. The prophet (saw) refused.The way i see it is that if she can sacrifice her entire culture and identity for the man she loves, i can reciprocate with alteast 10% of that for the woman i love.
What nulwala believes in is not religion, it is simply what is convenient at what time!!
Besides, why would you have a problem with bohras performing Sajda to the Dai and not have a problem with one of your bohris visiting a Hindu temple?