I agree with @Anonymous, best solution is not to explode the block. If the block does not fit your requirements you either need a new block or need to update your block to meet your requirements. As far as formatting goes, you should be able to get to what you want from the block.
If this is a one time thing then just selecting the entities to erase should be simple enough and be done.
The fundamental reason the attributes appear is because when you explode the block it detaches and the attributes from the block insert. Attributes are not stored in the block definition, attribute definitions are. The actual attributes are linked to the block insert. Burst takes a snap shot of attributes and values, it then explodes the block and then grabs what's left and then converts anything left as needed. The hidden components of the block that are stored as part of the actual block are deleted because the block definition itself is separate from the actual block. This is why once you select the non default state of a dynamic block it becomes an anonymous block. So that definition is what is exploded. The attributes are toggled in the background to hidden, but remain as part of the block. You could effectively write a routine to remove the extra attributes after the block is inserted, then process the burst command and it would behave as desired.
That may be more than you wanted to know, but good luck,
