One of the best ways to support an undercover missionary is to help them have a business. This provides them with a livelihood that is deemed legitimate by the government as well as a place of work where they can meet many people. As they do their work with honesty, thoroughness, generosity, and kindness, people have a chance to see the character of God before they even hear about Him. Undercover missionaries can then prayerfully discern who are open to the gospel and follow up discretely.
ASAP Ministries provides start-up funds for such businesses in countries we cannot name. Many of the church planters we support are laypeople who have additional jobs to supplement their stipend. God is seeking to finish His work everywhere, through various means.