Hey Scott,
There is already a “Run” command in the TCL bundle. That's probably the one you want to use. To get TextMate to recognize a TCL script by the #! line, you need to add a “firstLineMatch” rule to the grammar. For instance, the shell script grammar has this firstLineMatch:
firstLineMatch = '^#!.*(bash|zsh|sh|tcsh)';
You could add a similar first line match to the TCL grammar:
firstLineMatch = '^#!.*(tclsh)';
—Alex