Hey bobcat,
I know how you feel, I used to live off vegetable soup and it is no way to live!!
I don't suffer that often with migraines but use Rectogesic when I need to, it does cause a throbbing headache when first used but will ease off during the day, infact, the more you keep using the lesser the headaches, don't let it deter you from using as Recto can be quite effective with the pain.
I've never used Instillagel but found more info which may be useful to you here:
http://www.clinimed.co.uk/urology-continence-care/products/instillagel.aspx Try having a warm/hot bath after having a bowel movement and sit in it for 20-30 mins, this should bring blood flow to the area and soothe the pain a bit, most of us here swear by soaking in the bath 3-4 times a day.
Good Luck - Steve