(Cell phone tethering) Android hotspots & captive portals?

Let’s say I have an Android phone that creates a WiFi hotspot. Let’s say I want to share that with the public, but want them to see a captive portal page before they can browse the web (like how it works at a Starbucks). Is this possible?

No payment system or anything required, just want to show them a message before they connect, like “Sign this petition to get them to install wifi here!”