Baha'is do recognize that all the major religions have a Divine Origin but in this dispensation the privilege of financial assistance for Baha'i institutions rests solely with the friends...the Baha'is themselves. If the project is Baha'i inspired not a Baha'i institution then anyone can contribute... So you'll never have a Baha'i soliciting funds from non-Baha'is for a Baha'i institution.
You asked concerning some plans whereby funds could be gathered for the Temple. Shoghi Effendi believes that the best and noblest method is to have free donations that are made spontaneously and with the sense of making some sacrifice in furthering the Cause. It is with sacrifice that this Temple is to be built. This is the truly worthy method. This principle therefore excludes any method whereby the help of non-Bahá'ís is included. A Bahá'í Temple should be built by the Bahá'ís alone; it is not an ordinary humanitarian activity in which the help of any person could be solicited.
(In a letter written on behalf of Shoghi Effendi, 14 April 1932 to the Spiritual Assembly of Kenosha, Wisconsin, published in "Bahá'í News"[64] (July 1932), p. 4)