Hi,
Yes it is doable. After u select some text frame script will create new temporal indesign with same dimensions as text frame and after that export as pdf and after that close temporal indesign file without saving or if u need that that indesign script can save it also.
Generally I usually use Javascript for this, it run in back so it will be good for speed. I will send you detail explanation how to use that Script file and how to made some changes in the code if you want to do that. I assume that you already have experience with this kind of work. And if you are not do not worry you only need to upload javascript in Adobe programs and I run and for that u need a few seconds and couple of mouse clicks, after that script will run and u can do something more creative..
I have an experience of over seven years of work in Photoshop, Illustrator, InDesign, Acrobate, Adobe Lightroom, Microsoft Office (PowerPoint, Excel..), JavaScript associated with Adobe app, Python, Perl ... I am a very dedicated and diligent, so you can expect top quality.
Best regards,
Bojan