Assuming the glue is an alchemical sort of weapon, I think it would apply the same way multiple alchemist fires would: even though you [b]can[/b] hit someone with multiple alchemist fires to do more fire damage, the target still only needs to do one check in order to stop the fire on him. Additional hits from alchemist fire while on fire does nothing to make the fire more difficult to put out, either by increased DC or needing to take multiple actions to put out. That will only be needed if Brannor gets hit again by the glue bombs, thus requiring a new check for the condition he previous lost.

In short: two glue bombs are redundant since they both inflict restrain, and multiple stacks of restrain doesn’t amount to much unless they come from an alternative source instead of just the same type of glue bomb.