check 426.22 (NEC2002) The type of leads makes a diference about needing conduit or not. Splices with a direct burial coating would IMHO be accepted.
The buried conduit could be a Code violation if you look at 426.3
Also check 426.24 B and the reference to 300.15
Most installers are not aware of the requirement of 426.13. A warning sign must be posted to keep some contractor from cutting the concrete when the heat is turned on.
If it was easy, anyone could do it.