I asked this question here about a year ago and did not find any solution yet. As a workaround, we are asking people to enter the custom text into the order comments.
We are working on a project that requires exactly the same thing. Basically, we want to capture what the user enters in a text field in the same way that an option field is captured (typically used to say select the colour or size of a product). How can we do this?
There have been many conversations surrounding the topic of shop module and product options, <i>http://ez.no/content/advancedsearch?SearchText=Product+Options&SubTreeArray[]=308&SearchPageLimit=5</i>
I would very much recommend reading, almost all of it, twice :\
A problem that others may not consider is that all of the perception of problems is merely an illusion by a lack of understanding of the many ways available to account for your needs ... and quickly it all boils down to the <i>how</i> you really want to go about attempting to solve this to meet your own base needs because while I would recommend using the 'creating a custom content object based on selections from user and allowing the user to checkout this customer product...method' yet you may not be ready to tackle this on your own, you may prefer to hack a bit of the kernel instead or something else completely.
In looking back the most successful unique threads which share the most background in how they want to solve the problem, their background..
hth, <i>//kracker
(hed) Planet Earth - Back 2 Base X - Lets Ride</i>