I don't think they can. Current law in that respect does not apply to members of Congress, IIRC. Instead, Congress has decided that its members should:

1. Self-report on themselves, their spouses, their dependent children (why dependent children would be trading securities is beyond me, but OK.)

2. Be subject to a $200 fine for conflicts of interest or failure to report "in a timely manner"

3. Have the fine waived at the discretion of the House or Senate ethics committees

In other words, the rules they've applied to themselves are toothless.