You can add add this Perl script into you survey to set Q2=1 if Q1=1...
[% Begin Unverified Perl
End Unverified %]
*Note - I have assumed Q1 and Q2 are single response. Change their syntax if they are another question type (e.g. Q2_1, Q2_r1, etc.).
You may skip Q2 if Q1=1 and then add this script to the footer of a question after Q2. That should work.