CoRoutine to get async return value?

[kpjVideo]

Hello.
I'm not sure if I need a coroutine or what, but I'm trying to return the value of an asynchronous function.
The function always returns "nil" because it cannot finish before returning the correct value.

Code:
function ValidateStream( sURL )
if( !sURL ) then return end
local bGood = nil;

sound.PlayURL ( sURL, "3d", function( station )
if ( IsValid( station ) ) then
station:Stop()
bGood = true;
else
LocalPlayer():ChatPrint( "Invalid URL!" )
end
end )

return bGood;
end
Although "Invalid URL!" doesn't print, the function always returns nil.

Is there anyway around this? I remember someone using coroutines to circumvent this before, but I can't really figure out how they work in my context.
Any help is appreciated, Thanks