You certainly can place the inlet inside the outlet. What you will be getting, however, is subcooling in reverse. In this part of the cooling puzzle there is no change of phase. It is a pretty safe assumption that exposing the actively cooled inlet fluid to the fluid heated (albeit slightly) by the block will not result in a reduction in inlet fluid temperature.
I am unwilling to suggest that this will make a substantial difference in CPU cooling efficiency. This is similar to the whole "pump-rad-block vs. rad-pump-block" argument. It is beyond my "eyeballing"
skills to predict what effect this would have on overall fluid temperature. My guess is none. It will, however, reduce block-surface/coolant delta-T. This is not a good thing, but in this case almost certainly not disastrous. If this arrangement of tubing does indeed result in signifigantly improved insulation, it may even be beneficial.
I agree with Bill. Spend some more time on these forums and on some phase change forums, buy a few books, etc.. before you sink a bunch of money into this. It is much more cost effective in R&D to have a very good idea of what you will encounter before you just start building stuff.
Also, $300? Not likely. You are talking about some pretty good change here.
[Edited for error in expression]