The commodity issue is problematic. The problem is that most new world commodities (chillies, tomatoes, tobacco) grew very well indeed in parts of the world within the Asian trade network. Once someone brings them to Asia (which happened very swiftly) they will be adopted just as iotl where a minor agricultural crisis was spurred in china by the enthusiastic adoption of tobacco depleting previously rich agricultural land.
The reason for the scarcity of spice was that in most cases these couldn't be grown effectively in Europe. The same isn't true of New World crops and Asia as OTL shows.
Sorry to keep on throwing out obstacles but i think its important that we find the incentive. We need something concrete to get Asians across the Pacific.
The European adventurer scenario would still need to be underpinned by a concrete economic reason- they didn't go on adventures just for the fun of it.
While this is true, it bears mentioning that the lack of European plantations in Asia will make a big difference, both to the prices of some commodities seeked by Euros as well as the Asian native economies. No destruction of spice orchards in Maluku, for one thing. No coffee plantations as well as potatoes in West Java as well. This general situation will obstruct introduction of New world commodities into Asia to an extent. There are lots of ways this can play out.
Why Pacific ? Why can't Indians simply follow Europeans back to the Atlantic ? It's closer, and much easier too.
European adventures won't simply come and advice the Badshah or Maharaja to send a fleet to Europe and Americas. They will leave impact upon India gradually. They will become the first stone for crossfertilization between India and Europe. They will influence India intellectually, socially and culturally. Overtime, they can also develop this connection into two-ways relationship, where their influence will also stimulate Indian interest for going to western hemisphere as well. Why not ? Even without monopoly in Indian Ocean Europe isn't going to stay 15th century forever. They will grow into a level of sophistication that will attract Indian attention as well, with New World plunders. Especially after some european adventurers have brought few useful European innovations to India. Indians will also do the same to Europe, for sure.
Let's say some of these Indian adventurers get dragged quite deep into European and New World affairs, while still maintaining connection to the homeland. He'll might be the beginning of something big, depending on the issues of the time and opportunities present.
Under these conditions, I think one way would be to adjust Indian preference through European influence to a degree. For instance, I think it's not too farfetched to make Indians developing a taste for coffee grown in Brazil or Carribean instead of Africa or Middle East with PoD as early as 1500. That can be a good start to drag Indians westward. If that's not enough, then various Indian figures in the west, as an advisor or general of a European kingdom, or as pirates or notorious millionaires in the New World, should be able to do something or another to bring concrete Indian political and economic presence in western hemisphere. Let's figure this out together.