Another thing you can try:
Make a dummy builder unit without a model for every builder.
Make an ability based on Berserk for the builder, this will be the Advanced Building button.
When this ability is used, the dummy builder will be selected for the player, with its build menu open (use Force UI Key to open the build menu).
Make a trigger that, when the dummy unit is issued orders, the orders are given to the actual builder, and also a trigger that periodically moves the dummy builder to the actual builder.
Next, if you are using human powerbuilding, once a building starts you'll have to tell the advanced builder to stop, and order the actual builder to start building it.
If you aren't, which I'm assuming is the case since you have Warcraft 2.5 in your signature, you'll have to hide the actual builder unit until the building is finished/destroyed.