"Run As Administrator" does its job WITHOUT needing a password, is it a totally different animal from RUNAS ?
Yes, indeed. As confusing as MS chose to make UAC be, "run as administrator" does not mean "run under the administrator user account", but rather "run as the current user, but using its elevated token".
You may try something like...
psexec -accepteula -h cmd /c "%~0"
using PsExec from PsTools http://technet.microsoft.com/en-us/sysinternals/bb897553
Note that the "-h" switch is not documented on the PsExec page, yet shows up in its /? help:
'psexec /?' wrote:
-h If the target system is Vista or higher, has (sic) the process
run with the account's elevated token, if available.