<p>One of my Websites is on a Shared Hosting Provider, running either .net 2.0 or .net 3.0, but not 3.5 SP1.</p>

<p>I wonder if it would be possible to still use 3.5 SP1 by simply deploying all the 3.5 assemblies into the /bin Folder, since technically it's all still the 2.0 CLR.</p>

<p>I know that if my Host ever updates I have to remove them or else weird stuff can happen, and that I am driving into Unsupported-Territory at full speed, but is there any really big road sign that says "DON'T DO IT!" or even "That is not possible because of X"?</p>

<p>Primary reason is because I want to use ASP.net MVC and possibly ADO.net Entity Framework, but I do not want to make a contract with yet another Hosting provider.</p>

<p>Thanks!</p>

I'm pretty sure you can't do this, but googling on the following blogs may get you the definitive answer:
ScottGu
ScottHa
BradA
The problems would be, I think:
You want to load system.dll. Where does it look? does the GAC take precidence? (I think it does), therefore you get 2.0. So you have system.dll v2.0, and you try to use a DLL (eg system.web.mvc) which is bound to system.dll v3.5, but is only in you /bin.... it should explode loudly, not having the same contracts and the like.
Personally, I wouldn't try it, especially on production. But if you can take the site down for a while, give it a go. Worst case, you have to delete the files and re-upload the old site.
YMMV :)