If anyone has seen anything, especially this kind of thing in email discourse:
"thanks in advance for your help"
That would be really useful. I'm searching and getting no hits. The only relevant article I've found is the one below, which only mentions pre-emptive thanking in passing:
Puustinen, Minna, Josie Bernicot, and Alain Bert-Erboul. 2011. “Written Computer-Mediated Requests for Help by French-Speaking Students: An Analysis of Their Forms and Functions.” Learning and Instruction 21(2):281–89. Retrieved (http://dx.doi.org/10.1016/j.learninstruc.2010.07.005)
I've searched for 'pre-emptive thanking' (both hyphenated and not), 'anticipatory thanking' and 'thanks in advance' - if you think I'm using the wrong terminology, please also let me know!