Long-term planning help?

Wow!  First of all, let me say how happy I am to have found this site!!  I can't believe some of the stories and posts I have read... it's like I'm reading about my own marriage!  So thank you all for sharing your stories. 

As you can see from my username, I am a non-ADHD wife, married to a very very very ADHD husband.  He was diagnosed in kindergarten, and has tried all sorts of medication for the past 30 years.  So I am lucky compared to others here in that at least my husband acknowledges he has a problem.  Last year, we were at the breaking point, and I threatened to divorce him if he did not go to ADHD coaching, so he has finally started therapy, which seems to help a bit but we still have a long way to go.  I know therapy takes time, but I was wondering if anyone had any advice on how to get an ADHD partner to focus on long-term planning?

One of the biggest issues we have every year are our taxes.  I am the type of person who has their taxes done in January.  My husband is the person who files for an extension every year.  This year, he promised me that he would get his paperwork in order by January (latest February) so we could file by April 15.  Of course April came and went, and the only thing we filed was for an extension.  My husband owns a business and we really need an accountant to do our taxes for us, otherwise I would just do them for both of us so they would get done.  Unfortunately, doing his business taxes and my personal taxes is out of my league.  After we filed for an extension, my husband did NOTHING to find an accountant (he refused to let me find one, because he says he needs to interview them since they will be doing his business taxes...).  Now, it is September and we still have no accountant, and no plan for doing the taxes.  And on top of that, every week when I have tried to get him to go to the office to work on the taxes, he schedules a sales trip, or a sales show or something.  I tried to explain that he needs to focus on the fact that our taxes need to get done, but he is only able to focus on the short term sales trips.  For him, October seems like such a long way away, that he can't think about it.  Everytime a store asks him to come do a sales presentation, he immediately agrees, instead of thinking about the fact that we have a huge tax deadline loom over us.  He has already booked himself on sales trips for most of September, so it is unclear how he will ever get his paperwork in order by October to file our taxes. 

How do I get him to focus on this longer-term task that needs to get done and reprioritize away from these short-term things?  Normally, I would just pay the penalty and file separately, but this year the penalty for filing "married, filing sepatately" will be close to $20,000 for me.  I don't have that kind of extra money sitting around to send to the IRS, because I foolishly believed my husband when he promised me he would be ready to file our taxes 9 months ago. 

I am really paying the price for being married to someone with ADHD!!! literally!  Help!?