Thanks for that. I've managed to make Solution 2 work, so I think my final workflow ends up like this:
1) Create and run survey #1 as normal (users self register, create tokens, etc)
2) Create survey #2:
- new tokens table
- extended attribute for every answer you want to reuse from survey #1
- to refer to a participant's previous answer, you insert {TOKEN:ATTRIBUTE_4}
- to pre-fill an answer, you add this (in "source" mode):
<script>
$(document).ready(function()
{
$("#answer168948X4X5").text('{TOKEN:ATTRIBUTE_4}');
});
</script>
where "168948" is survey #2's id, 4 is the group id, and 5 is the question ID.
3) Export answers from survey #1
4) Export the (blank) tokens table from survey #1 as CSV, to get the header structure.
5) Use Excel magic to populate the CSV file in 4 with answers from 3
6) Import the freshly populated CSV file as tokens for survey #2
7) Activate the survey, send out invitations, hurray!
The workflow is a little bit messy, but it doesn't involve modifying any code, so I'm happy.
(I haven't actually tested steps 3, 4, 5 and 6 - but that should work, right?)