Ah, found a thread with an answer by BB, to thick glass, now...

http://www.renderosity.com/mod/forumpro/showthread.php?message_id=3817511&ebot_calc_page#message_3817511

Which is pretty much what I thought it was going to be actually... I've read dozens of similar threads. Just not in this exact context... and I hadn't initially figured out the correlation I guess.

I've subsituted a fresnel_blend node into the basic "Reflect and Refract nodes, blended off the alt_diffuse" setup... and I suspect that's really now doing the trick (at least as far as I need it to) in combination with the convex lens, within the magnifying glass prop I'm using.

Set the IOR of the fresnel_blend node to 1.523 and then adjusting the IOR of the refract node seems to work to increase or decrease the effect... as does adjusting the radius of curvature via the morph I added.

Now... about that "visible aberation" that EnglishBob mentioned... maybe just a displacement or bump using a clouds or spots node? Either that or I make another, assymetrical, morph I guess.

I'll maybe play with that next I guess... ;)