@santa sangria , First of all the communication I would use is "not deliberate". I often use that even if in midfield, best preceding by "no...".
I am not sure if you are in fact following the process right. You could not communicate this until you have an outcome (not necessarily stopping game) as with the 'immidiate' clarification. So in practice the player should either score or create a GSO within at most two touches or I'd say a stretched one second. If that happens you blow the whistle and give the FK. If it doesn't then you can do the communication and two possibilities thereafter. Nothing comes of the attack which is all good. A goal is scored after a few seconds or longer. You allow that and justify it by saying the accidental handball was in the build up and did not directly create the goal. It will be a hard sell but we have those every now and then.
I have had this twice, once in February before the break and once last weekend. Neither time I had time to blow the whistle before ball was out of play.
First one was a one on one with keeper and the close range shot bounced of keeper into attacker's hand and then to his feet for a tap in. Blew the whistle and disallowed the goal. Restart with DFK.
Second one was all very quick. Deflection off a defender to an attacker's arm then on his foot. He was clearly in a GSO but hit the post from close range and out. Goal kick was the better option for restart there.