Custom layer questions

I'm playing around with some of the "Custom Layer" db routines.  Namely:

addCustomText

I'm using it to add block alias texts to my top-level fences.  My design has top-level instance names with very long names.  In a full window with all the design "fitted" to the screen, I can't see any of the names.  In order to fix this, I wrote a script that takes a very long name and gives it an alias.  For instance:

my_design_has_very_long_hinst_names_AAA_inst0

...would have an alias:

AAA0

I'm trying to center the text in the middle of the fence but it would be nice if I could place the center of the text custom layer in the center of the fence.  Is there a way to get the bounding box associated with the text object?  Is there a way to move a text object that's already been placed or do I need to delete it and re-add it later?

Thx,

JG

P.S. I haven't been able to reproduce but it seems like having too many custom text objects is really bogging down X.