Absolutely and where we're directed to or where we can we do, but alas egates aren't available at all airports yet ( like here in our home city) so sometimes it's still the old third degree for no particular reason, personally I treat such check points as a mere administrative annoyance and almost walk myself through barely stopping, but my bf doesn't yet have that confidence.
I have to agree with MM here Oliver, I think you're thinking WAY to fay ahead in the process so far and if others experiences are anything to go by you've still a very big uphill task on your hands to even GET the visa and if you are successful then Passport control would be the LAST of my worries as by that point the decision to admit has already been made and all passport control are doing assuming that nothing is untoward is basically box ticking his arrival in to the Country when admitting your friend. GETTING the visa is the hard part, passport control is ( in my mind anyway) a total non issue almost.
As others have said the main task for you / him is to show sound reasons that he will return to Thailand ( good job, responsibilities at home, short dated return ticket - if you wanted to risk buying that ticket before getting the visa this is - personally I wouldn't as I think his chances may be slim depending on his circumstances). But hey you can only try, but others have tried before you and been turned down for little reason it seems, Meanwhile the UK certainly seems to be admitting just about ANYONE else these days EXCEPT cute Thai guys !! Talk about the system TOTALLY getting it wrong ! Just tell them he's a 35 year old Muslim Asylum seeker but pretending to be 14 with no papers and he should be fine it seems !
Best of luck anyway and do be sure to keep us all updated as to your progress ( and costs) just in case the "mood" has changed somewhere in government and it's now easier to bring friends from Asia ( but I doubt it unfortunately :-( )