Can i declare a attack without having attack dice in my armament?

You can do the step 1 of the attack, Declare target, but as soon as you reach step 2 the attack is canceled as you can't gather any dice.
Maay I ask why you want to declare an attack this way?

Because im working on a custom ability that reads as "Instead of attacking" and it will be both on unarmed and armed squadrons.

Well Jendon does not need to be in range of an enemy squad to pass his attack to someone else. Check that wording and use similar.