Suppose, hypothetically, the party leaders decided that they wanted Sanders over Clinton. Would they be able to make this happen?

I read somewhere that the Democrats have a lot of delegates that are chosen because they are state or local party officials, and that these delegates are not bound to any particular candidate, and that these delegates are heavily favoring Clinton.

I'm curious because there is a good chance that Trump will not get enough delegates to win the Republican nomination on the first vote (Cruz and Kasich definitely cannot get enough). If that happens, it is plausible that Kasich could get the nomination. Kasich is the only one of him, Trump, and Cruz that consistently beats Clinton in polls and in a contested convention a lot of Republicans will be arguing that there is no point in nominating someone who cannot win.

The Democratic convention occurs shortly after the Republican convention ends. If Kasich does get the nomination I wonder if those unbound Democratic delegates might switch from Clinton to Sanders, because Sanders consistently trounces all Republicans in polls, and Sanders would also probably do a better job of getting out the youth vote which could help Democrats regain control of Congress.