That is a very interesting questions.  Here is my guess...

The IRS lien attaches to all property and rights to property of the taxpayer.  This includes future interests, contingent interests, and executory contracts. In this example, Joe Blow certainly had a right to property.  So, I believe that the IRS could go after something.  But, I don't think that the IRS has a lien on the real estate because it doesn't appear Joe Blow held a legal or equitable interest in the property.. 

The IRS might be able to get a lien on the real estate if they could prove that Joe Blow has an equitable interest in the property, held in the name of family members.  But, I think that interest would be limited to the percentage value that Joe Blow contributed to the purchase price.

I think the IRS would have a lien on the proceeds from selling his right to buy the property.  In this case, since it was family, I think the IRS would have a lien on the value of the that right.  I'm not sure how much that would be worth.  Maybe the amount of the down payment he paid to secure the right... or maybe the difference between the bid price and fair market value of the property. 

You will have to let us know if your client insures the title.

Best,
Robert.