Is it legal to run with your athlete during an Ironman?

Question

I will be cheering on a family member at an Ironman race later this year and as an amateur runner myself, I think it would be fun to run a few miles with him and cheer him on. I would not take anything from aid stations or run through the finish. Is it against race regulations for a spectator to be on the course in that manner? Is it bad form even if legal?
(Running with an athlete like this may be confused with pacing?)

From: IRONMAN competition rules:

Section 6.03 FINISH LINE CONDUCT Friends, family members, and/or other spectators are not permitted to cross the finish line or enter the finish chute with participating athletes. (Please note: IRONMAN desires for each athlete to be able to celebrate his/her accomplishment without risking the safety of other Event participants, volunteers, and/or spectators). Athletes who choose not to respect the foregoing finish line policy will be disqualified.

But I could run part of the course with him?

Answer 1

Certainly you wouldn't be allowed to cross the finish line with them based on the rule you cited, but as ckett said running with them in general could be considered outside assistance as a pacer.

From the Ironman rules:

2.01 (i) Compete without receiving assistance from other parties (other than from Race Referees, Race Officials, and other athletes in accordance with Section 2.02). Receiving assistance (other than in accordance with Section 2.02) will result in disqualification;

Though it could result in just a 30 or 60 second time penalty if you stop immediately when told. From appendix A:

If it is possible to amend and return to the original situation then a 30 or 60 Second Time Penalty (as applicable) Time Penalty will be assessed, If not: DSQ

There isn't anything explicitly disallowing it in the rules, so it would be worth asking one of the officials in one of the Athlete Briefing that occurs on the day before the race. That would be the definintive answer.