Adding a polyA tail to a vector?????

[Greg Nattrass]

I need to generate a polyA tail of approx 70 adenosines for a Xenopus
expression vector. Would Terminal deoxynucleotidyl Transferase (TdT) be
the enzyme to use for this application. I have used it to tail cDNA but
am unsure as to how I should use it on plasmid DNA. 

Does anyone know how efficient TdT is at adding dATP to blunt dsDNA or
even a recessed 3'OH generated by RE digestion?

Has anyone used a similar or better strategy to add a polyA tail? 

Thanks for any help
Greg Nattrass